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SCKHCE HID TECKIOSY MISI 

Ubrxy of Congress 


SUMMARY TECHNICAL REPORT 
OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 



This document contains information affecting the national defense of 
the United States within the meaning of the Espionage Act, 50 U. S. C., 
31 and 32, as amended. Its transmission or the revelation of its con¬ 
tents in any manner to an unauthorized person is prohibited by law. 

This volume is classified CONFIDENTIAL in accordance with security 
regulations of the War and Navy Departments because certain chap¬ 
ters contain material which was CONFIDENTIAL at the date of 
printing. Other chapters may have had a lower classification or none. 
The reader is advised to consult the War and Navy agencies listed on 
the reverse of this page for the current classification of any material. 


AL 




Manuscript and illustrations for this volume were prepared 
for publication by the Summary Reports Group of the Co¬ 
lumbia University Division of War Research under contract 
OEMsr-1131 with the Office of Scientific Research and De¬ 
velopment. This volume was printed and bound by the 
Columbia University Press. 

Distribution of the Summary Technical Report of NDRC 
has been made by the War and Navy Departments. Inquiries 
concerning the availability and distribution of the Summary 
Technical Report volumes and microfilmed and other refer¬ 
ence material should be addressed to the War Department 
Library, Room 1A-522, The Pentagon, Washington 25, D. C., 
or to the Office of Naval Research, Navy Department, Atten¬ 
tion: Reports and Documents Section, Washington 25, D. C. 


Copy No. 



This volume, like the seventy others of the Summary Tech¬ 
nical Report of NDRC, has been written, edited, and printed 
under great pressure. Inevitably there are errors which have 
slipped past Division readers and proofreaders. There may 
be errors of fact not known at time of printing. The author 
has not been able to follow through his writing to the final 
page proof. 

Please report errors to: 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION (STR ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports 
and sent to recipients of the volume. Your help will make 
this book more useful to other readers and will be of great 
value in preparing any revisions. 




SUMMARY TECHNICAL REPORT OF DIVISION 17, NDRC 


VOLUME 2 


COMPASSES, ODOGRAPHS, 
COMBAT ACOUSTICS, AND 
SONIC DECEPTION 


OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 


NATIONAL DEFENSE RESEARCH COMMITTEE 


DIVISION 17 



Return r 0 


Dr *ry of 


Com 


Wess 



WASHINGTON, D. C., 1946 * 



NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative 1 

Frank B. Jewett Navy Representative 2 

Karl T. Compton Commissioner of Patents 3 

Irvin Stewart, Executive Secretary 

2 Navy representatives in order of service: 

Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 
Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 
Commodore H. A. Schade 

3 Commissioners of Patents in order of service: 

Conway P. Coe Casper W. Ooms 


^ Army representatives in order of service : 


Maj. Gen. G. V. Strong 
Maj. Gen. R. C. Moore 
Maj. Gen. C. C. Williams 
Brig. Gen. W. A. Wood, Jr. 

Col. E. A. 


Col. L. A. Denson 
Col. P. R. Faymonville 
Brig. Gen. E. A. Regnier 
Col. M. M. Irvine 
Routheau 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suit¬ 
able projects and research programs on the instrumen¬ 
talities of warfare, together with contract facilities for 
carrying out these projects and programs, and (2) to 
administer the technical and scientific work of the con¬ 
tracts. More specifically, NDRC functioned by initiating 
research projects on requests from the Army or the 
Navy, or on requests from an allied government trans¬ 
mitted through the Liaison Office of OSRD, or on its 
own considered initiative as a result of the experience 
of its members. Proposals prepared by the Division, 
Panel, or Committee for research contracts for perform¬ 
ance of the work involved in such projects were first re¬ 
viewed by NDRC, and if approved, recommended to the 
Director of OSRD. Upon approval of a proposal by the 
Director, a contract permitting maximum flexibility of 
scientific effort was arranged. The business aspects of 
the contract, including such matters as materials, clear¬ 
ances, vouchers, patents, priorities, legal matters, and 
administration of patent matters were handled by the 
Executive Secretary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 

These were: 

Division A—Armor and Ordnance 
Division B—Bombs, Fuels, Gases, & Chemical Problems 
Division C—Communication and Transportation 
Division D—Detection, Controls, and Instruments 
Division E—Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three 
administrative divisions, panels, or committees were 
created, each with a chief selected on the basis of his 
outstanding work in the particular field. The NDRC 
members then became a reviewing and advisory group 
to the Director of OSRD. The final organization was 
as follows: 


Division 1—Ballistic Research 

Division 2—Effects of Impact and Explosion 

Division 3—Rocket Ordnance 

Division 4—Ordnance Accessories 

Division 5 —New Missiles 

Division 6—Sub-Surface Warfare 

Division 7—Fire Control 

Division 8—Explosives 

Division 9—Chemistry 

Division 10—Absorbents and Aerosols 

Division 11—Chemical Engineering 

Division 12—Transportation 

Division 13—Electrical Communication 

Division 14—Radar 

Division 15—Radio Coordination 

Division 16—Optics and Camouflage 

Division 17—Physics 

Division 18—War Metallurgy 

Division 19—Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 


IV 







NDRC FOREWORD 


As events of the years preceding 1940 re- 
jT\_ vealed more and more clearly the serious¬ 
ness of the world situation, many scientists in 
this country came to realize the need of organ¬ 
izing scientific research for service in a national 
emergency. Recommendations which they made 
to the White House were given careful and 
sympathetic attention, and as a result the Na¬ 
tional Defense Research Committee [NDRC] 
was formed by Executive Order of the Presi¬ 
dent in the summer of 1940. The members of 
NDRC, appointed by the President, were in¬ 
structed to supplement the work of the Army 
and the Navy in the development of the in¬ 
strumentalities of war. A year later, upon the 
establishment of the Office of Scientific Research 
and Development [OSRD], NDRC became one 
of its units. 

The Summary Technical Report of NDRC is 
a conscientious effort on the part of NDRC to 
summarize and evaluate its work and to present 
it in a useful and permanent form. It comprises 
some seventy volumes broken into groups cor¬ 
responding to the NDRC Divisions, Panels, and 
Committees. 

The Summary Technical Report of each Divi¬ 
sion, Panel, or Committee is an integral survey 
of the work of that group. The first volume of 
each group’s report contains a summary of the 
report, stating the problems presented and the 
philosophy of attacking them, and summarizing 
the results of the research, development, and 
training activities undertaken. Some volumes 
may be “state of the art” treatises covering 
subjects to which various research groups have 
contributed information. Others may contain 
descriptions of devices developed in the labora¬ 
tories. A master index of all these divisional, 
panel, and committee reports which together 
constitute the Summary Technical Report of 
NDRC is contained in a separate volume, which 
also includes the index of a microfilm record 
of pertinent technical laboratory reports and 
reference material. 

Some of the NDRC-sponsored researches 
which had been declassified by the end of 1945 
were of sufficient popular interest that it was 
found desirable to report them in the form of 
monographs, such as the series on radar by 
Division 14 and the monograph on sampling 
inspection by the Applied Mathematics Panel. 
Since the material treated in them is not dupli¬ 
cated in the Summary Technical Report of 
NDRC, the monographs are an important part 


of the story of these aspects of NDRC research. 

In contrast to the information on radar, 
which is of widespread interest and much of 
which is released to the public, the research on 
subsurface warfare is largely classified and is 
of general interest to a more restricted group. 
As a consequence, the report of Division 6 is 
found almost entirely in its Summary Technical 
Report, which runs to over twenty volumes. 
The extent of the work of a division cannot 
therefore be judged solely by the number of 
volumes devoted to it in the Summary Tech¬ 
nical Report of NDRC: account must be taken 
of the monographs and available reports pub¬ 
lished elsewhere. 

The research work of Division 17 included a 
wide variety of projects, ranging from the de¬ 
tection of land mines to the characteristics of 
the human ear, from helium purity indica¬ 
tors to the telemetering of strain gauges, from 
odographs to sound-ranging devices. It is a 
tribute to the broad knowledge of the Division 
Chiefs—Paul Klopsteg and, later, George R. 
Harrison—and to the versatility of the men 
who worked under them that so diverse a pro¬ 
gram was handled so competently. 

A considerable portion of the work of Divi¬ 
sion 17 had to do with the shattering noise of 
modern war, and answers were sought and sup¬ 
plied to such questions as: How much noise can 
a human being stand? What clues must the 
human ear have in order to understand a 
spoken message? How much distortion can be 
tolerated? These and other phases of the Divi¬ 
sion’s work are dealt with in the Summary 
Technical Report prepared under the direction 
of the Division Chief and authorized by him 
for publication. 

The diversity of the Division’s projects made 
it inevitable that its staff should be composed 
of men with many types of scientific training 
and that the Division should draw on contrac¬ 
tors with a wide range of experience and skills. 
The studies of noise, in particular, meant that 
the technical staff must include physicists, 
acousticians, and psychologists. For the ability 
and devotion of these men of many aptitudes 
we express our gratitude. 

Vannevar Bush, Director 
Office of Scientific Research and Development 

J. B. Conant, Chairman 
National Defense Research Committee 


































* 














































FOREWORD 


T he applied physics division of the Office 
of Scientific Research and Development 
[OSRD] was organized late in 1942 under the 
chairmanship of Dr. Paul E. Klopsteg, who was 
responsible for the work of the Division until 
shortly before the completion of its work when 
other duties required his full attention. Most 
of the projects which had been initiated by the 
Instruments Section of the National Defense 
Research Committee [NDRC] during 1940 and 
1941 and which were not concerned with optics 
were turned over to the Applied Physics Divi¬ 
sion on its inauguration. Dr. Klopsteg as Chief 
and Dr. E. A. Eckhardt as Deputy Chief went 
with them from the Instruments Section to the 
new Division. 

The Summary Technical Report which is pre¬ 
sented in these volumes thus covers the accom¬ 
plishments of projects set up by both Section 
D-3 and Division 17. The work of the Division 
covered a very wide range of fields. The term 
Applied Physics served in lieu of a more de¬ 
scriptive name for a Division which was in fact 
the one to which was assigned any scientific 


problem which did not properly come under one 
of the other divisions of NDRC. 

Actually the Division was an association of 
three Sections having rather dissimilar respon¬ 
sibilities and fields of activity. In setting up 
these Sections it was necessary to group the 
projects already under way into a small num¬ 
ber of coherent categories, and those chosen 
were Sound, Electricity, and General Instru¬ 
mentation. The work of the Division consisted 
entirely of the integrated efforts of these three 
Sections, whose membership will be found listed 
on a succeeding page. 

For more detailed reports on the technical 
work of the Division than are contained here¬ 
with the detailed contractors’ reports of Divi¬ 
sion 17 should be consulted, and appropriate 
reference to these have been made throughout 
the present volumes. The results obtained are 
also presented in less technical form in that 
volume of the history of OSRD entitled Optics 
and Applied Physics in World War II. 

George R. Harrison 
Chief, Division 17 


LC REGULATION: BEFORE SERVICING 
OR REPRODUCING ANY PART OF THIS 
DOCUMENT, ALL CLASSIFI CATION 
MABKINCS MUST BE CANCELLED. 


Return To 


sntstt 


m is #® 1 m 

Lfcrarv Con ^ ress 


r- 'f ' • 


INFLUENTIAL < 











PREFACE 


T he research and development program of 
Division 17, NDRC, was concerned with 
those problems in physics not specifically cov¬ 
ered in other Divisions of NDRC. As the result, 
the Division fell heir to a myriad of miscellane¬ 
ous problems of a physical nature which, in 
themselves, were not often interrelated. It would 
have been exceedingly difficult, if not impossible, 
for Division 17 to set up within itself a sufficient 
number of Sections to deal specifically with all 
the various classes of problems which fell under 
their jurisdiction. Therefore, the projects of the 
Division were assigned to one of three Sections 
—Section 17.1, Instruments; Section 17.2, Elec¬ 
trical Equipment; and Section 17.3, Acoustics— 
whose broad titles permitted a general, even if 
somewhat loose, classification. It was not always 
easy to decide, at times, under which of these 
three broad categories a given project should 
be placed. In these cases, considerations such as 
immediate convenience and availability of ex¬ 
perienced personnel were often the determining 
factors. 

The Summary Technical Report describing 
the activities of Division 17 is presented in four 
volumes. In an attempt to achieve a little greater 
uniformity of subject matter, the projects were 
organized within the various volumes without 
regard to their Section classification. Conse¬ 
quently, there is, on the whole, little relation¬ 
ship between volume and Section number. Be¬ 
cause of the varied problems dealt with in the 
Division’s program, very little continuity is to 
be found from chapter to chapter in any volume. 
Each chapter attempts to summarize independ¬ 
ently the results of a particular project. 

Since there were a large number of diversified 
projects in Division 17, it was obviously im¬ 
possible to do justice to each, even in summary. 
It is not intended that the importance of any 
project described herein should be judged by 
the amount of page space allotted to it. Natu¬ 
rally, certain problems involved more research 
and development than others before they could 
be brought to a successful conclusion. In many 
cases, this is reflected in the Summary Technical 
Report. On the other hand, the presentation of 
the projects may mirror the enthusiasm (or lack 
of it) of the individual author at the time of 
writing. Therefore, the reader who desires more 
than a broad panorama of the Division’s activ¬ 
ities is referred to the Microfilm Index for more 
complete details. 


This second volume of the Division 17 Sum¬ 
mary Technical Report is divided into two parts. 
Part I contains six chapters dealing with vari¬ 
ous general types of instruments for combat use. 
The instrumentation described in these chapters 
differs from that in Volume 4 in that this latter 
volume described instruments of a laboratory 
or training nature. 

The seven chapters comprising Part II of this 
volume deal with combat acoustics, sonic decep¬ 
tion and simulation. Although the subject 
matter of the individual chapters varies some¬ 
what, the underlying problems, theory, and 
techniques encountered throughout are similar. 
In this way, then, there is a distinct correlation 
between the projects presented in Part II. 

The reader may wonder why the material in 
Part II, which deals essentially with sound, was 
not placed in Volume 3, which is solely devoted 
to problems of sound. In the first place, Volume 
3 of this Report represents the work of one 
particular laboratory whereas the projects out¬ 
lined in Part II of Volume 2 are the contribu¬ 
tions from several laboratories. The second 
reason for not including the chapters of Part 
II in Volume 3 is that the Volume 3 subject 
matter is closely coordinated and there seemed 
no logical reason for destroying the continuity 
of a volume that was complete in itself. 

Every reasonable effort has been made to 
keep this volume free from error, scientific or 
otherwise. Should some creep in, the authors 
and editor would be grateful to have them called 
to their attention. Although this is a technical 
report, by its very nature it is inevitable that 
opinions other than scientific may be expressed. 
The reader is reminded that these do not neces¬ 
sarily reflect the opinions of the authors, editor, 
nor NDRC as a whole, but rather those of Di¬ 
vision 17. 

It should be borne in mind that the material 
contained in these chapters represents a sum¬ 
mary of the combined efforts of many men who 
labored so faithfully for so long for so little 
personal recognition. Although certain of these 
men, as authors, bore the brunt of preparing 
this volume, many others contributed freely of 
their time to read authors’ manuscripts, for 
accuracy, Division and NDRC policy, and 
offered valuable suggestions and criticisms, 
answered innumerable questions. To these men, 
then, as well as to the authors, the editor of 
this volume expresses his deep appreciation. 


CONFIDENTIAL 


IX 




X 


PREFACE 


Lest the mention by name of all those who 
contributed to the preparation of this volume be 
considered as a listing in minor hall of fame, it 
has been purposely avoided. The name of the 
author will be found under the chapter titles. 
Where no name appears, the editor, with the 


help of innumerable Division members, Con¬ 
tractor employees, and friends, has prepared 
the summary from the various contractors’ re¬ 
ports. 

Chas. E. Waring 
E ditor 


FIDENTIAI4 







CONTENTS 


PART I 

GENERAL INSTRUMENTA TION 

CHAPTER PAGE 

1 Compasses and Odographs by L. L. Nettleton . 3 

2 T-58 Photoflash Fuze by George E. Beggs, Jr .58 

3 Oximeters.68 

4 Radio Chronometer Comparator.73 

5 Fuel Quantity Gauges.75 

6 Combustion Efficiency Indicator for Naval Vessels by F. L. Yost 80 

PART II 

SOUND TRANSMISSION AND INSTRUMENTATION 

7 Ultrasonic Signaling by Harold K. Schilling .87 

8 Jungle Acoustics by Carl F. Eyring .92 

9 Attenuation of Sound in the Atmosphere by V. O. Knudsen 106 

10 Injurious Effects of Exposure to Loud Tones and Noises . 110 

11 High-Intensity Sound Produced by Chain Explosions . . . 113 

12 Sound Simulation and Masking.117 

13 Mobile Loudspeaking Systems for Deception and Decoy . . 131 

Glossary.171 

Bibliography.173 

OSRD Appointees.178 

Contract Numbers.180 

Service Project Numbers.183 

Index.185 


















PART I 

GENERAL INSTRUMENTATION 









Chapter 1 

COMPASSES AND ODOGRAPHS 


By L. L. Nettleton 


11 SUMMARY OF COMPASS AND 
ODOGRAPH DEVELOPMENT 

Historical Summary 

T he development covered by this report was 
originated by a suggestion early in 1941 
from the Army Engineer Board to the National 
Defense Research Committee [NDRC] that in¬ 
vestigations be made for two purposes, i.e., (1) 
to determine the feasibility of using magnetic 
compasses in heavily armored vehicles, partic¬ 
ularly tanks, and (2) if such compasses were 
feasible, the development of an automatic 
course-plotting or dead-reckoning tracing de¬ 
vice. 

The required investigations and tests were 
carried out over a period of nearly five years 
under contracts originally let in 1941 and 1942 
between NDRC and four different scientific and 
engineering organizations and with the cooper¬ 
ation of both the Army and the Navy. Most of 
the fundamental development, the establish¬ 
ment of working principles, and first field tests 
were carried out under Section C-3. The work 
was continued and some contracts were ex¬ 
tended when the project was transferred to 
Section 17.1 of NDRC in December 1942. The 
production of equipment in quantity was han¬ 
dled by direct Army contracts. Many improve¬ 
ments and extensions and the experimental ap¬ 
plications to military equipment were handled 
largely by cooperation between NDRC, its con¬ 
tractors, and the Services. 

The development was quite continuous, and 
no distinction is made in this report between 
those parts which were under the auspices of 
Section C-3 and those under Section 17.1. 

1,1,8 General Evaluation of the Project 

The work on compasses under these contracts 
has resulted in much useful information regard¬ 
ing methods of compensation and has enabled 
the Services to extend the use and improve the 


performance of magnetic compasses in many 
applications heretofore believed impossible. 
Magnetic compasses have been made to perform 
satisfactorily both inside and outside of tanks, 
command cars, armored cars, and jeeps. The 
Navy Department has made use of the informa¬ 
tion to redesign and standardize compasses for 
all classes of craft. 

The odograph has been applied successfully 
on a substantial scale to reconnaissance mis¬ 
sions, to mapping, to fire control, and ranging 
problems, and has proved particularly useful 
in jeep installations. It has been used success¬ 
fully in landing craft and similar small marine 
installations, in DUKW’s, and in various other 
types of specialized vehicles, such as the Weasel. 
The airborne unit contributed materially to the 
reconnaissance missions preceding the inva¬ 
sions of the Philippines and to other Southwest 
Pacific missions. While the Air Forces’ use of 
the equipment was limited, the contribution was 
nonetheless important. The pedograph proved 
particularly successful in the rough mapping 
of strange terrain by infantry personnel. 

As mentioned, the demand for a vehicular 
odograph originated in the Engineer Board, 
Corps of Engineers, U. S. Army. Its develop¬ 
ment was strongly supported by both the Army 
and the Navy. The adaptation of the device to 
aircraft was visualized by NDRC and its con¬ 
tractors and was carried forward by them on 
the basis of definite interest by several Army 
units and in anticipation of more general Serv¬ 
ice support. This never materialized. It is be¬ 
lieved that lack of merit of the device and ab¬ 
sence of need for its functions were not basically 
the cause for the failure of active Service inter¬ 
est to develop. 

1,1,8 Summary of Developments under 
the Project 

Early in 1941, NDRC entered into a contract 
(NDCrc-187) with the Department of Terres- 


3 


4 


COMPASSES AND ODOGRAPHS 


trial Magnetism [DTM], Carnegie Institution 
of Washington for compass and odograph in¬ 
vestigations. The possibility of satisfactory 
compensation of a compass, even when inside 
of a tank, was demonstrated, and the develop¬ 
ment of an automatic mapping device was then 
undertaken. The first such device was made by 
DTM, the integrating element in the odograph 
being a gear with variable stepped teeth. This 
original instrument included many parts from 
a Monroe calculating machine and was first 
demonstrated in a station wagon in January 
1942. 

Shortly after this demonstration, Contracts 
OEMsr-340 and OEMsr-426 were entered into 
between NDRC and the Monroe Calculating 
Machine Company [Monroe] and International 
Business Machines Corporation [IBM], respec¬ 
tively, for manufacture of pilot models of odo¬ 
graph instruments. Monroe undertook to engi¬ 
neer for manufacture the original DTM inte¬ 
grator and, later, the DTM compass, which 
became known as the standard compass. IBM 
developed an independent integrator based on 
a variable ratchet drive. The pilot models of 
these integrators were tested in various land 
vehicles and their military usefulness deter¬ 
mined to the extent that the Army negotiated 
contracts with both Monroe and IBM for manu¬ 
facture of compasses and integrators in consid¬ 
erable numbers. 

At the request of the Army, Contract OEMsr- 
1121 was entered into between NDRC and Gen¬ 
eral Motors Research Laboratory [GM] for the 
development of an inductor-type compass. The 
original purpose was to investigate an inde¬ 
pendent compass type and possible alternative 
source of supply. Later it was found that the 
performance of the GM compass was much su¬ 
perior to that of the standard compass under 
conditions of severe shock and vibration. In the 
meantime, the standard compass was greatly 
improved until its performance was nearly as 
good as that of the inductor compass, except 
under the most severe conditions. The GM in¬ 
ductor compass was never manufactured in 
quantity, either for use as a compass alone or 
in connection with odograph installations, be¬ 
cause (1) the improved DTM compass uses 
simpler electric accessories which had already 


been adapted to numerous odograph installa¬ 
tions, (2) the Service problems of restandard¬ 
ization would be severe, and (3) the remaining 
performance difference was rather small. 

Along with the compass developments, Gen¬ 
eral Motors developed a magnetic eraser to con¬ 
trol semipermanent magnetization of vehicles 
and thereby reduce this, by far the most trou¬ 
blesome source of compass errors. Extensive 
tests made by the contractor on a tank and a 
jeep showed substantial overall reduction in 
compass errors to be available from the use of 
the magnetic eraser. It was apparently believed 
by the Services that the devices required would 
be too complicated and that their power re¬ 
quirements would be too high to justify their 
application. The NDRC representatives did not 
concur in this view, and it is felt that, in any 
future use of magnetic compasses in tanks, the 
related work of General Motors could be re¬ 
viewed and extended with profit. 

The success of the vehicular device led to the 
development of the airborne odograph which 
had been contemplated early in the program. 
IBM, originally at their own expense and later 
in cooperation with NDRC, developed an inte¬ 
grator using a friction disk drive with variably 
positioned pickup rollers moving over the face 
of a disk driven at a rate proportional to the 
speed of the plane. This integrator was orig¬ 
inally adapted to the Schwien true airspeed 
meter and later to the British and Pioneer air 
mileage units for giving the rotation of the disk 
proportional to the air distance traveled and 
to the Pioneer gyrostabilized fluxgate compass 
for giving the direction. (These accessory de¬ 
vices had been developed previously for other 
purposes.) The integrator also incorporates a 
second disk drive assembly (a second inte¬ 
grator) by which correction for wind drift can 
be set so as to give position with respect to the 
ground. A relatively large map is made on a 
remote, electrically driven plotting table, and 
one or more such tables plotting at different 
scales, if desired, may be used at locations inde¬ 
pendent of the other parts of the installation. 

This airborne odograph was tested in several 
types of aircraft and gave quite satisfactory 
performance. These devices were manufactured 
and used in rather limited number. 





REQUIRED ELEMENTS AND FUNCTIONS PERFORMED 


5 


Odograph installations were made also in 
various boats and amphibious vehicles. This 
required the development of a water-driven 
speedometer and associated servomechanism to 
operate the odograph without drawing appre¬ 
ciable power from the impeller unit in the 
water. Application to amphibious vehicles 
(DUKW) also required a means of shifting the 
odograph drive from the water element to an 
ordinary speedometer cable when changing 
from water to land operation. 

Other developments toward the end of the 
program were the pedograph and the step- 
writer. The pedograph is a relatively simple 
instrument carried by a man; the distance com¬ 
ponent is given by a thread which rotates a 
pulley as it is pulled out of the instrument and 
the direction by a manually operated compass 
follower. The step-writer is a somewhat simpler 
device in which the distance is given by im¬ 
pulses from a connection to the operator’s leg 
and the direction by manually turning the map¬ 
ping paper to keep it aligned with the compass. 

The compass development made possible com¬ 
passes which were manufactured by tens of 
thousands for use in many kinds of Army and 
Navy vehicles. Also, some 2,000 land odographs 
and some 50 aerial odographs were made. These 
developments have obvious peacetime applica¬ 
tions and have led to actual or contemplated use 
in improved automobile and ship compasses and 
use of vehicular odographs in exploration and 
mapping. 


12 REQUIRED ELEMENTS AND 
FUNCTIONS PERFORMED 

1,2,1 Requirement of Compass, 

Distance, Integrating, and 
Power Supply Units 

In order to plot the course of a vehicle, it is 
necessary that we know at all times its direc¬ 
tion and distance from some reference or start¬ 
ing point. This requirement will be fulfilled if, 
at all times, the north or south component and 
the east or west component of the distance 
traveled are known. Thus it is essential that the 


instrument for course plotting contain the fol¬ 
lowing elements: 

1. A compass of some kind which gives a ref¬ 
erence direction with respect to which the car¬ 
dinal component of each element of travel may 
be resolved. 

2. A log or odometer element (or a speed¬ 
measuring element) from which increments of 
distance traveled may be determined (either 
directly in terms of distance, or indirectly in 
terms of speed multiplied by time). 

3. An integrator which combines the indica¬ 
tions from the compass and the distance- or 
speed-measuring unit in such a way that each 
increment in distance is resolved into its com¬ 
ponents, one parallel to and one perpendicular 
to the reference direction. These components of 
motion operate two counters by which the in¬ 
stantaneous coordinates of position are shown 
and two perpendicular screws which move a 
pencil to make a continuous trace of the path 
traveled by the vehicle. 

4. A power supply unit which converts the 
available primary electric source (usually ve¬ 
hicle batteries) into the voltages and frequen¬ 
cies required for the various electrical opera¬ 
tions. 

In any particular application, a complete odo¬ 
graph installation will be made up in various 
ways, depending upon the type of the vehicle 
and use for which it is intended. The choice of 
compass, distance (or speed), and integrator 
combination will be dictated by the circum¬ 
stances surrounding the application. Each of 
the four elements (compass, log, integrator, 
and power supply) is usually a more or less 
independent unit, and the different elements 
are electrically or mechanically connected in 
various ways, which are dictated by magnetic, 
mechanical, and electrical conditions of the ve¬ 
hicle. The plotting table may be either a part 
of the integrator unit to which it is connected 
through appropriate gearing, or it may be op¬ 
erated electrically at a point remote from the 
integrator unit itself. 

A Typical Odograph Installation 

Figure 1 shows an installation in a 1,4-ton 
4x4 truck (jeep) which was probably the Army 
vehicle most frequently carrying odograph 


(JONFIDE 





6 


COMPASSES AND ODOGRAPHS 


equipment because of the relative simplicity of 
its installation and because of its utility in 
reconnaissance. The units of the installation, 



Figure 1 . Land odograph, Model M-l, installed 
in a %-ton 4x4 truck (jeep). 

comprising compass, odograph with plotting 
table, and power pack, are evident in the pic¬ 
ture. The units themselves and the connections 



Figure 2. Schematic arrangement of odograph 
components and connections for installation on a 
jeep. 


between them are shown diagrammatically by 
Figure 2, which also indicates the speedometer 
cable connection from which the distance input 


is obtained. Figure 3 shows a map made with 
an installation of the type shown by Figures 1 
and 2. 


13 COMPASSES AND COMPASS 

COMPENSATION 

1,31 General Requirements 

Compass Principles Available 

There are two general types of compass 
which might be applied to an odograph. These 
are, first, the gyroscopic compass and, second, 
the magnetic. The magnetic compass may be 



M,LE 

Figure 3. Map from odograph installations in a 
jeep, showing mapped trace and actual roads 
traveled. 

either the ordinary magnetic needle or an in¬ 
ductor type which uses the principle of a trans¬ 
former with a core of high-permeability mate¬ 
rial so that the induced or secondary voltage is 
controlled by the effect of external magnetic 
fields on the core. Each principle has certain 
advantages and disadvantages which must be 
considered in connection with odograph appli¬ 
cations. 

Gyroscopic Compasses 

The gyroscopic compass has the advantage 
that it is not affected by its environment, that 


CONFIDENTIAL 































COMPASSES AND COMPASS COMPENSATION 


7 


is to say, its operation does not depend upon 
masses of magnetic material in its neighbor¬ 
hood. It has two disadvantages, i.e., first, its 
mechanical complication involving an air or elec¬ 
tric supply to drive it at a very high speed, and 
second (and a much more formidable one), an 
ordinary gyroscope will maintain a given azi¬ 
muth or direction of orientation only within 
limits, as there is always a tendency for pre¬ 
cession, which produces a drift of the gyroscope 
away from its originally established orienta¬ 
tion. This drift is such that it is not possible 
to use a simple gyroscope as a primary direction 
reference, for it requires that the gyroscope be 
reset occasionally (resetting at about 15-minute 
intervals is used on airplane applications) with 
respect to some other direction reference. The 
use of a self-directing or north-seeking gyro¬ 
scopic compass, such as is used on ships, would 
hardly be feasible on small or land vehicles. A 
gyroscopic ship’s compass is a comparatively 
large and elaborate installation and has a very 
slow period, so that it requires operation over 
long periods of time to give reliable direction 
indications. It is very doubtful that such a com¬ 
pass could be made to operate under the very 
severe conditions of shock and rapid changes in 
direction that must be met in many odograph 
applications. It could be used on large ships or 
other vehicles where the compass itself would 
operate satisfactorily for, in principle, any com¬ 
pass indication could be applied to an odograph. 

Magnetic Compasses and Magnetic 
Disturbances 

The essential indicating element of a mag¬ 
netic compass is very simple, but any magnetic 
compass (either a simple magnetic needle or an 
inductor type) is subject to disturbances from 
magnetizable parts of any vehicle in which it 
may be installed and from the magnetic fields 
of any electric auxiliaries with which the ve¬ 
hicle may be equipped. Means (described in the 
following section) have been developed by 
which compensation for these effects can be 
attained to a degree which permits satisfactory 
compass operation on most vehicles. Most of the 
inaccuracies of operation and limits to the pre¬ 
cision of compasses and of odograph maps result 
from the fact that the magnetic state of the ve¬ 


hicle is variable. This change with time of the 
magnetic condition of the vehicle and especially 
in vehicles with large magnetic mass, such as 
tanks, requires that the compensation be checked 
frequently. These difficulties must be attacked by 
reducing or stabilizing the magnetic disturb¬ 
ances of the vehicle, and particularly that part 
of it containing the compass. No gain can result 
from improving the compass itself until the 
magnetic environment is controlled. 

Compass Followers 

Some sort of servomechanism must be con¬ 
trolled by the compass and be “slaved” so as to 
follow its indication, but must operate in such 
a way (through light or electric impulses) that 
it does not affect the primary direction indica¬ 
tion resulting from the action of the earth’s 
magnetic field on the compass. In all the odo¬ 
graph installations, the servomechanism is op¬ 
erated in such a way that the compass follower 
tends to overshoot a position of balance so that 
it “hunts” about a position controlled by the 
directing magnetic field. As will be pointed out 
later, this hunting is a necessary characteristic 
for two reasons: (1) it serves to interpolate 
between discrete steps of increment in the inte¬ 
grator mechanism, and (2) it serves to elim¬ 
inate any effects of backlash or looseness in the 
gears and mechanical connections between the 
compass follower and the elements in the inte¬ 
grator which it controls. 


1-3 ’ 2 Compass Compensation 

Introduction 

The use of the magnetic compass in connec¬ 
tion with an odograph installation implies that 
the compass will maintain its north-south in¬ 
dication, controlled by the horizontal component 
of the earth’s magnetic field, without regard 
to the direction of heading or attitude of the 
vehicle on which it is mounted. As the vehicle 
itself practically always contains some iron 
parts which are magnetized permanently, semi¬ 
permanently, and/or by induction, the compass 
indication will, in general, be affected by dis¬ 
turbances arising from such magnetization, and 
the elimination of such disturbances by com- 


^mgg^TIAl. 






8 


COMPASSES AND ODOGRAPHS 


pensation is one of the major problems in main¬ 
taining a reasonably precise magnetic reference 
direction. 

The general theory of compass compensation 
has been worked out in considerable detail in 
connection with the use of magnetic compasses 
on shipboard. Certain parts of this theory are 
directly applicable to the compensation of the 
compasses on ground vehicles, but, in general, 
the conditions to be met are more severe, the 
problem is more complicated, and the degree of 
compensation obtainable is less exact than on 
shipboard. 1511 

Semicircular Error 

There are two types of disturbance which 
must be compensated. The first arises from per¬ 
manent magnetic fields which are set up by 
magnetic material of the vehicle which is per¬ 
manently magnetized and therefore retains its 
direction and magnitude of magnetization with 
respect to the vehicle as the vehicle changes its 
heading and thereby its relation to the earth’s 
magnetic field. This type of disturbance causes 
the semicircular error, so called because its 
effects vary with the sine and cosine of the 
angle of heading (since these magnetic effects, 
being carried with the vehicle, change their re¬ 
lation to the orientation of the compass as the 
heading is changed). The semicircular error 
may be compensated by properly positioned and 
adjusted permanent magnets placed in the vi¬ 
cinity of the compass and so situated that the 
fields which they produce at the compass mag¬ 
net are equal and opposite to the permanent 
fields produced by the permanently magnetized 
parts of the vehicle. Two sets of adjustable 
permanent magnets (see Figures 4 and 5), giv¬ 
ing fields in perpendicular (N-S and E-W) di¬ 
rections, are required to compensate for the 
horizontal components of permanent magnetiza¬ 
tion. As is pointed out later, a third set, to give 
a vertical component, is needed to compensate 
for the magnetic component which becomes 
active when the vehicle is not level. 

Quadrantal Error 

The second type of magnetic disturbance 
comes from “soft” magnetic materials in which 
magnetization is induced by the earth’s mag¬ 


netic field. The disturbance at the compass pro¬ 
duced by such fields varies with the relation of 
the earth’s field to the vehicle and therefore 
varies as the heading of the vehicle is changed. 
Such induced fields lead to the quadrantal error, 
so called because their effects vary with the sine 
and cosine of twice the angle of heading. Com¬ 
pensation for this type of error is obtained by 
the use of soft iron masses in the vicinity of 
the compass, so placed that the fields at the 



compensating system. 

compass resulting from the magnetization of 
these masses by the earth’s field (and by the 
compass needle itself in some applications) are 
equal and opposite to the field produced by 
induction in other parts of the vehicle. The 
standard procedure for quadrantal compensa¬ 
tion as developed for ship’s compasses has been 
to place rather large, soft iron spheres (or 
cylinders) near the compass, the magnetization 
of these spheres resulting from induction by 


Confidential 


























COMPASSES AND COMPASS COMPENSATION 


9 


the earth’s field. However, the spheres required 
are quite bulky, as they must be placed at suffi¬ 
cient distances from the compass so that they 
will not be materially affected by the magnetic 
field of the compass needle itself. 

A procedure developed in connection with the 
compass project was the use of much smaller 
masses of magnetically soft material placed 




ROTATABLE BAR MAGNET 


SCREW-TYPE HEELING 
COMPENSATOR 


COMPENSATOR COVER 


DRAWER 
COMPENSATOR 


SCREW-TYPE 

HOZIZONTAL 

COMPENSATOR 


NUTS AND 
COLLARS 


SPIDER-TYPE 

COMPENSATOR 


COMMUTATOR COVER 


Figure 5. Pictures of compass parts. 

relatively close to the compass so that the mag¬ 
netization induced in these masses is largely 
that produced by the magnetic field of the 
compass needle itself. Analysis has shown and 
practice has confirmed that quite satisfactory 
compensation of the quadrantal error can be 
obtained in this way. In practice, the compen¬ 
sation is achieved by a small, horizontal, eight¬ 
armed spider with the arms oriented in cardinal 


and midcardinal azimuths with respect to the 
coordinate system of the vehicle. (See Figure 4.) 
Each arm carries Permalloy collars (or wash¬ 
ers) held in place by huts on the arms of the 
spider. By adjusting the number and position of 
the Permalloy washers on the several arms of 
the spider and following out a fixed procedure 
of making the adjustments with the vehicle in 
certain definite headings, quite effective com¬ 
pensation for quadrantal errors is obtained. 51 

Heeling and Pitching Errors 

The consideration of semicircular and quad¬ 
rantal compensation as outlined above is based 
on the assumption that the compass itself and 
the vehicle are substantially level. Other errors 
are induced by heeling (i.e., lateral tilt of a 
vehicle, as, for instance, when driving on the 
side of a crowned road) and pitching (whether 
going uphill or downhill). It turns out that, 
while the heeling errors may be quite large, 
effective compensation may be achieved by the 
use of permanent magnets producing a vertical 
field at the compass. It also turns out that the 
pitching error is partially compensated by the 
heeling correction and that, if the compass is 
placed where the quadrantal deviation is small, 
the residual pitching error is usually negligible. 

Subpermanent Magnetization 

By the use of three sets of magnets, such as 
are indicated in Figures 4 and 5, giving prop¬ 
erly adjusted permanent field components at 
the compass in the three principal directions, 
the semicircular and heeling errors may be 
quite effectively compensated, and, by the use 
of properly placed small masses of easily mag¬ 
netizable material near the compass, the quad¬ 
rantal error is quite completely compensated. 
Thus the compass may be made to give the 
same readings within one degree or less in all 
headings as long as the magnetic condition of 
the vehicle remains the same as that for which 
the compensation adjustments were made. 

a This principle cannot be applied to inductor (trans¬ 
former) type compasses because there is no magnetized 
needle to affect the Permalloy compensators, so larger, 
soft iron cylinders or spheres must be used (see Figure 
34, Section 1.6.2). However, these iron masses can be 
smaller than for ordinary ship’s compass compensation 
because there ie no magnetic needle to magnetize them 
as it changes its position. 





10 


COMPASSES AND ODOGRAPHS 


The most serious source of compass error is 
in the subpermanent magnetization. This is de¬ 
fined as magnetization of the induced type in 
parts of the vehicle which are not completely 
soft magnetically, so that some of the magne¬ 
tization induced when in one heading is re¬ 
tained when the heading is changed. Such mag¬ 
netization may be greatly modified by mechan¬ 
ical shock. It turns out that the subpermanent 
magnetization affects the semicircular compen¬ 
sation much more than the quadrantal. Since 
the changes in subpermanent magnetization 
depend upon the mechanical shocks to which 
the vehicle is subjected, the heading of the ve¬ 
hicle at the time of such shocks, and subsequent 
changes in heading, none of which can be an¬ 
ticipated, errors due to these disturbances can¬ 
not be compensated. However, there are means 
by which they can be substantially reduced. 

Certain of the effects of subpermanent mag¬ 
netization can be reduced by proper selection 
of the position of the compass with respect to 
the vehicle, particularly in placing the compass 
in a position which is symmetrical with respect 
to the magnetizable masses. Extensive tests of 
a compass mounted in various positions on a 
jeep and with certain modifications of the struc¬ 
ture of the vehicle itself were carried out 15b to 
analyze in some detail the causes and sources 
of these subpermanent magnetic disturbances. 
The only way to completely eliminate such dis¬ 
turbances would be to have the compass several 
feet away from any magnetizable part of the 
vehicle, which, of course, is quite impractical. 
It is feasible, however, to find places where the 
disturbances due to subpermanent magnetiza¬ 
tion are small enough so that a practical com¬ 
pass installation may be made, and such installa¬ 
tions have been accomplished in a large variety 
of military vehicles. The subpermanent magne¬ 
tization remains, however, the largest single 
source of error in vehicular compasses and in 
the production of odograph maps, and the dif¬ 
ferences in the effectiveness of odograph instal¬ 
lations on various vehicles and the great diffi¬ 
culty in achieving really good odograph per¬ 
formance in tanks arise from these subperma¬ 
nent effects. No degree of perfection of the 
compass itself or of compensation will take care 
of these effects permanently, and'in heavy ve¬ 


hicles, such as tanks, they require readjust¬ 
ments of the compensation at intervals of, at 
most, a few days or a few hundred miles of 
driving to maintain tolerable performance. 

Magnetic Fields of Tanks and 
Other Vehicles 

In connection with the development of mag¬ 
netic mines against tanks and of possible means 
of countering such mines, extensive measure¬ 
ments were made of the magnetic fields of tanks 
and other vehicles. This work, carried out by 
DTM, was not part of the Odograph and Com¬ 
pass project and was under an entirely separate 
contract (OEMsr-151). However, some of the 
instruments and the measurements carried out 
in this connection 14 are pertinent to magnetic 
compass development in that they are concerned 
with the same physical (i.e., magnetic) prop¬ 
erties of the vehicle which are encountered in 
the problems of compass compensation. 

The instrument developed is a permeability- 
type, remote-indicating magnetometer. A six- 
channel unit was made which would indicate 
and record simultaneously the variations of the 
magnetic field in any chosen direction as picked 
up by each of the six sensitive elements. 

Extensive measurements were made of the 
magnetic fields, particularly under tanks, and 
detailed mathematical analyses carried out, pri¬ 
marily from the standpoint of the design of 
magnetic firing devices for mines. The purpose 
of mentioning this work here is simply to call 
attention to the methods of measurement of 
magnetic fields and the many profiles and maps 
of field patterns which are contained in the 
report, 14 as a review of this work should be very 
useful if it again becomes important to consider 
means of improving compass performance in 
heavily armored vehicles. 


Demagnetization of Military 
Vehicles 

It has been mentioned that the subpermanent 
magnetic effects constitute a serious difficulty 
in operating a magnetic compass in a vehicle 
containing massive iron parts. An attack on 
this problem was made by the construction of 






COMPASSES AND COMPASS COMPENSATION 


11 


a magnetic eraser which was designed to de¬ 
magnetize the vehicle in such a way that the 
subpermanent magnetic effects would be re¬ 
duced and/or stabilized. 

The Magnetic Eraser 

The general principle of the magnetic eraser 
is that of maintaining a repeated cycle of alter¬ 
nating magnetic fields in different directions in 
certain selected parts of the vehicle rather than 
in trying to completely demagnetize the dis¬ 
turbing iron parts. Experiments 19 show that, 
when an attempt is made to demagnetize iron 
pieces by gradually reducing the strength of 
an alternating field, a point is reached at which 
the residual magnetization is no longer reversed 
by the reversals of the field and the magnetiza¬ 
tion therefore can be reduced only to a certain 
minimum. The situation is somewhat analogous 
to rocking a coin back and forth in the bottom 
of a rounded bowl. If the bowl is tilted strongly 
from one side to the other, the coin will slide 
from side to side corresponding to the reversals 
of magnetization which result from reversals 
of a strong magnetic field. If the angle through 
which the bowl is tilted is gradually reduced, 
a point will be reached at which friction is not 
overcome, and the coin will cease to slide back 
and forth with each oscillation and will no 
longer move relative to the bowl. This degree 
of tilting corresponds to the magnetic field 
strength at which reversals of magnetization 
cease to occur, and the magnetization corre¬ 
sponding to this point is the minimum which 
can be reached by reversals of a decreasing 
magnetic field. In tests with steel bars and 
blocks and large welded steel boxes, it was 
found that the field strength at which the 
reversals of magnetization cease is about 50 
oersteds and that the remaining magnetization 
is erratic and of the order of 10 to 20 gauss. 

The magnetic eraser operates on a continued 
cycle of reversals of magnetic fields of sufficient 
strength so that the magnetization of the iron 
follows the reversals. This corresponds to con¬ 
trolling the mean position of the coin in the 
tilting bowl so that it tends to oscillate about 
the center rather than trying to make it come 
to rest at the center. 

It was found that considerable reduction in 


the disturbances due to semipermanent mag¬ 
netization could be expected if the vehicle were 
carried through a systematic series of magne¬ 
tizations by coils placed so that a magnetizing 
field could be induced in each of the three prin¬ 
cipal coordinates and current switched through 
these coils in such a way as to apply the mag¬ 
netic field in a repeated cycle of magnetization 
in directions N, E, Up, S, W, Down, and re¬ 
peated. The power supply, switching, and coils 
to supply this repeated cycle of magnetization 
constitute the magnetic eraser. 

Applications and Tests of the 
Magnetic Eraser 

In order to apply the magnetic eraser to mili¬ 
tary vehicles, coils are put either about towel 

n 



Figure 6. Diagram of magnetic eraser switch. 


bars (which are iron bars welded to the struc¬ 
ture especially for the application of the mag¬ 
netic eraser) or around existing parts of the 
structure. The installation of the magnetic 
eraser consists of suitable coils and bars so that 
magnetization can be induced in the vehicle in 
horizontal, transverse, and vertical directions, 
a suitable motor-driven switch for switching 
the current among the coils to give the desired 
cycle of magnetization, and a suitable power 


i IDENTIAL 1 









12 


COMPASSES AND ODOGRAPHS 




vm mm 


1 o 1 


1 





Figure 7. Photograph of magnetic eraser switch 


. 






COMPASSES AND COMPASS COMPENSATION 


13 


supply (storage batteries). A special switch, 
Figures 6 and 7, was designed for the purpose 
which would carry through the erasing cycle at 
frequencies up to 100 per minute. 

Magnetic eraser installations were made on 
a jeep and an M-5 tank. For some of the coils, 
advantage was taken of parts of the structure, 
such as the bumper on a jeep (Figure 8). 

Extensive tests were made of the operation 
of the compass and odograph in the jeep and 



Figure 8. Installation of magnetic eraser on 
jeep. 


tank with and without the magnetic eraser op¬ 
erating and with it operating at different fre¬ 
quencies. The operation of the eraser should be 
better for heavier currents and lower frequen¬ 
cies, but the disturbances to the compass caused 
directly by the fields of the eraser would be less 
at lower currents and higher frequencies. As a 
compromise, the tank installation was operated 
at about 100 cycles per minute and required an 
average current of 4 amperes at 12 volts. Maps 
were made and compass changes determined 21 
with and without the magnetic eraser operating 
and with the tank subjected to magnetic and 


mechanical disturbances (welding on the tank, 
pounding when in different headings, and driv¬ 
ing over rough roads). The net effect of these 
tests is the indication that the magnetic eraser 
would reduce the disturbance due to semiper¬ 
manent magnetization and the necessity of re¬ 
compensation by approximately 50 per cent. 

The magnetic eraser development was car¬ 
ried only far enough to indicate that it had 
some promise. There was no point to carrying 
it further until application to a specific vehicle 
was to be undertaken. A decision to this effect 
was never made. 


The DTM Compass 

The compass described in this section was 
developed by DTM in 1941-1942 and was manu¬ 
factured by Monroe in considerable quantity, 
both for use as a simple vehicular compass and 
for odograph installations. It became known as 
the standard compass. 

The simplest compass is a pivoted magnet, 
oriented by the horizontal component of the 
earth’s magnetic field. Consideration of effects 
of tilting and of shock requires that the moving 
system be suspended from a single pivot and 
that it be heavily damped; these requirements 
led to the development of an instrument, the 
moving system of which comprises, fundamen¬ 
tally, a magnet system suspended from a sin¬ 
gle pivot and partially immersed in a damping 
fluid. 

The Servomechanism 

In order that the compass may actuate the 
odograph element without any reaction on the 
compass itself which would disturb its indica¬ 
tions, the controlling element of the servomech¬ 
anism or compass follower is a beam of light 
from a small lamp, which is reflected from a 
double mirror carried by the compass (Fig¬ 
ure 9) and as indicated schematically in Fig¬ 
ure 10. The double mirror, with two surfaces at 
right angles (see Figure 9), is used so that the 
light beam is reflected back in the same place 
as the lamp, independently of the angle between 
the lamp and the plane of the compass card 
(which will change with tilt of the vehicle). 


\ FIDENTIAI/ 







14 


COMPASSES AND ODOGRAPHS 


The lamp and two flanking photoelectric cells 
are carried together on a rotatable ring with 
peripheral teeth through which it is driven by 
a small pinion connected by a flexible shaft to 
the odograph. The two photoelectric cells con¬ 
trol thyratron tubes (also mounted on the 
rotating ring) ; these thyratron tubes control 
the current through the coils of a magnetic 
clutch in the odograph integrator. The electric 



Figure 9. Section of standard compass showing 
lamp and mirror system. 


connections are such that, after one of the 
photoelectric cells has been activated by reflec¬ 
tion of light upon it, current continues to pass 
through the associated thyratron and clutch 
coil until the other cell is activated. The relation 
of the clutch and associated motor-driven gear¬ 
ing (Figure 10) is such that, when light falls 
on one phototube and activates the associated 
thyratron and clutch magnet, the entire ring 
assembly carrying photocells and lamp is ro¬ 
tated so that it brings the other photocell 
toward the beam of light reflected from the 


compass mirror. For example, when light fol¬ 
lowing the dashed lines of the diagram enters 
the left photocell, the associated thyratron is 
energized as the other is rendered nonconduc- 
tive, so that the clutch magnet coil connected 
to the left thyratron takes control and shifts 
the clutch to reverse the rotation of the gear 
train and flexible shaft so that the ring carry¬ 
ing the photocell assembly is now shifted to the 
left until the right-hand photocell is activated 
by light reflected from the compass mirror. 
Then the other clutch magnet takes control as 
the first is released, the gear train is again 
reversed, and the cycle repeated. 

The result of this arrangement is a continual 
shifting of the clutch magnets and oscillation 
of the ring carrying the lamp and phototubes 
back and forth, so that alternately one and then 
the other of the phototubes receives light re¬ 
flected from the compass mirror. In the land 
vehicle installation, the angle of rotation be¬ 
tween the positions of reversal is approximately 
10 degrees, and the frequency of this oscillation 
or hunting is approximately 75 complete cycles 
per minute. It is evident that, if the compass 
card is rotated relative to the case by a change 
in heading of the vehicle, the center of oscilla¬ 
tion of the ring will shift along with the posi¬ 
tion of the compass, so that the outer ring con¬ 
tinuously oscillates or hunts about an average 
position controlled by the position of the com¬ 
pass itself. It is further evident that, since the 
power is derived from the motor and associated 
magnetic clutches, the torque available to drive 
the compass follower carrying the photocells 
and any other connected apparatus, particu¬ 
larly the sine disk of the integrator element, 
is limited only by the design of the mechanical 
system, and does not in any way disturb the 
compass needle itself, for its only connection to 
the mechanical system is through the beam of 
light reflected from its mirror. 

The Compensating System 

The compensating system of the compass as¬ 
sembly is shown particularly by previously 
mentioned Figures 4 and 5. The variable parts 
of the permanent magnetic fields required are 
produced and conveniently adjusted by pairs of 
permanent magnets, each rotatable and geared 


CONFIDENTIAL 
































































COMPASSES AND COMPASS COMPENSATION 


15 



Figure 10. Compass and integrating mechanism in combination. 


^confidential/ 














































































































































16 


COMPASSES AND ODOGRAPHS 


together so that, as they are adjusted, the two 
magnets of a pair rotate in opposite directions. 
This serves to produce a magnetic field which 
is variable in strength but constant in direc¬ 
tion, as the moment but not the orientation of 


chamber, 2, which holds vertical bar magnets; 
two rotatable pairs of magnets, 4, for fine ad¬ 
justment of N-S and E-W horizontal compensa¬ 
tions; a rotatable pair, 1, for fine adjustment 
of vertical compensation; an 8-armed spider, 5, 


RUNS WITH MONROE UNIT 



START 


NO. /-STANDARD COMPASS } 35 MPH 


FINISH 



RUNS WITH IBM UNIT 



Figure 11. Odograph records for comparison of standard and improved compass. Traces are for run of 
1.6 miles over rough corduroy road. 


the resultant magnet formed by the combina¬ 
tion of the two is varied when the two are ro¬ 
tated in this manner. The compensating system 
includes: a small drawer, 3, Figure 4, which 
holds N-S and E-W horizontal bar magnets; a 


carrying Permalloy collars, 7, for quadrantal 
compensation. 

Approximate compensation for permanent 
magnetization is made by placing a proper 
combination of si'nall bar magnets in the drawer 


CONFIDENTIAL 







COMPASSES AND COMPASS COMPENSATION 


17 


and in the vertical chamber and making the fine 
adjustments with the rotatable pairs or screw- 
type compensators. Quadrantal compensation is 
made by adjusting the position and number of 
Permalloy collars on the arms of the spider. 
The entire compensation procedure is rather 
complicated, requiring making a certain sys¬ 
tematic series of readings and recordings of 
deviations in various headings of the vehicle. 
For routine use, forms are supplied on which 
the various steps and recordings are clearly in¬ 
dicated (some 55 entries 35 * 1 ) so that relatively 
untrained personnel can carry out the necessary 
procedure. 

Reduction of Vibration Effects 
on Compasses 

The first model of the so-called standard ve¬ 
hicular odograph compass had part of the mov¬ 
ing mechanism suspended in a damping liquid. 
It was found that this compass was very se¬ 
verely affected by strong vibration of the ve¬ 
hicle, such as might be encountered, for in¬ 
stance, in driving a jeep over a corduroy road. 
This effect is due to purely mechanical effects 
resulting largely from asymmetrical force com¬ 
ponents caused by the reaction of swirling 
damping fluid on the moving system such that, 
when violently agitated, the compass would be 
turned far from its proper azimuth and, in some 
cases, would make one or more complete revolu¬ 
tions. Tests were made 150 of various types of 
antivibration or shockproof mountings of the 
compass itself, but none was found which did 
not transmit vibrations at some speed of the 
vehicle which very seriously affected the com¬ 
pass performance, and it was found that better 
overall results were obtained when the compass 
was mounted rigidly on the vehicle. An im¬ 
proved model of the compass was then devel¬ 
oped in which the damping vanes were rede¬ 
signed to eliminate the asymmetrical forces and 
in which most of the weight of the moving sys¬ 
tem was buoyed up by the liquid in the damp¬ 
ing-fluid chamber. This led to very greatly 
improved performance of the compass and cor¬ 
responding odograph traces in tests over rough 
roads (see Figure 11). It was this last improve¬ 


ment that finally gave a magnetic compass 
which could be quite satisfactorily applied to an 
odograph installation on ground vehicles. 

It may be reiterated here that, no matter how 
perfect the compass itself may be, it is subject 
to limitations imposed by any instability of its 
magnetic environment and consequent require¬ 
ments of recompensation resulting primarily 
from subpermanent magnetization. It is these 
limitations which make it seem entirely impos¬ 
sible to attain the limit of precision in odograph 
maps of the order of 1 in 300, which was set at 
the time of the original suggestions by the mili¬ 
tary, but performance approaching a precision 
of 1 in 100 can be regularly obtained in all but 
the most severe circumstances. 


The General Motors Inductor 
Compass 

The General Motors project for the develop¬ 
ment of a compass was set up, at the request of 
the Army, to produce an alternative compass 
for use on land vehicles which would operate on 
different principles from the standard compass 
and which might, if necessary, lead to an alter¬ 
native source of supply. 

Principles of Operation 

The instrument as developed consists of an 
inductor-type element responsive to the earth’s 
magnetic field together with a servomechanism 
which keeps the sensitive element oriented into 
the position of zero output, that is, a position 
perpendicular to the magnetic field. The output 
of the servomechanism can be connected to the 
standard vehicular odograph. 

The principle of operation of the sensitive 
element is indicated by Figures 12 and 13. The 
direction-sensitive element consists of two pri¬ 
mary coils, L-l and L-2, Figure 12, wound in 
opposite directions upon a Mu-metal core, M, 
with a single secondary coil, L- 3. The operation 
depends upon the fact that the Mu-metal core 
becomes magnetically saturated for small fields 
and therefore is completely saturated for each 
half cycle of the primary magnetizing current, 
as indicated by Figure 13. The voltage induced 
in the secondary coil depends upon the change 







18 


COMPASSES AND ODOGRAPHS 


of flux in the Mu-metal core. If there is no ex¬ 
ternal magnetizing field, the change in flux in 
the two halves of the coil within the primary 
windings L-l and L-2 is about a zero position, 
which is symmetrical with respect to the two 
sides of the magnetization curve (A^ and A</>/, 
Figure 13, are equal), so that the voltages in¬ 
duced in the secondary coil, L-3, by the two pri¬ 
mary coils, are equal and opposite and the out¬ 
put voltage in L-3 is zero. However, if there is a 
magnetic field which affects the Mu-metal core, 



Figure 12. Principle of direction-sensitive head, 
inductor compass. 


the axis about which the magnetization takes 
place is displaced toward one side or the other 
of the magnetization curve (say to the dashed 
horizontal line of Figure 13), so that the range 
of magnetization from the axis to saturation is 
different in the two primary coils (A <p 2 and 
A <f> 2 ' are different) ; the induced voltages in the 
two halves of the secondary coil no longer bal¬ 
ance, so that there is a net output in the second¬ 
ary coil, L-3. The magnetic characteristics of 
Mu-metal are such that a field of the order of 
magnitude of that of the earth will magnetize 
it to a considerable fraction of saturation. For 
this reason, the output voltage in the coil, L-3, 
is responsive to the orientation of the Mu-metal 
core with respect to the earth’s field; the mag¬ 
nitude of the voltage of L-3 depends upon the 
azimuth of the core with respect to the magnetic 
meridian, and the phase of this voltage with re¬ 
spect to the exciting current in coils L-l and L-2 
reverses when the direction of magnetization of 
the Mu-metal core reverses. Therefore, the out¬ 
put of the coil L-3 passes through zero and 
changes sign as the Mu-metal core is oriented 
through the magnetic E-W direction. 

The Servomechanism 

If a servomechanism is provided which is re¬ 
sponsive to the output of the secondary coil in 


such a way that it orients the sensitive element 
in the direction to give zero output, the compass 
element will be maintained in a magnetic E-W 
direction. Power derived from the servomecha¬ 
nism can then be used to drive the azimuth ele¬ 
ment of an odograph integrator and the com¬ 
pass will give the proper direction control to the 
odograph. The direction-sensitive head contain¬ 
ing the Mu-metal bar is suspended on gimbals 
in a damping fluid with the suspension being 
carried on a rotatable head driven by the servo¬ 
mechanism. Electric contacts to the sensitive 
element are carried through slip rings. 

The servomechanism as developed for this 
instrument is a moderately elaborate device 243 
which involves an amplifier and thyratron tubes 



Figure 13. Magnetization curve for Mu-metal 
core of direction-sensitive head. 


which control coils of electromagnetic clutches. 
The proper phase and time relations between 
the output of the compass element and the thy- 
raton tubes are obtained through a motor- 
driven multiple contactor which controls the 
primary current in coils L-l and L-2 and the 
grids of the thyratron tubes, so that, when the 
direction of magnetization of the Mu-metal 
core (and therefore the phase of the output 
voltage with respect to the primary current) is 
in one direction, one of the thyratron tubes is 


CONFIDENTIAL 



























COMPASSES AND COMPASS COMPENSATION 


19 


operated, and, when the phase of the output 
voltage is reversed, the other is operated. Thus, 
when the azimuth of the direction-sensitive 
head is off on one side from an E-W direction, 
one of the thyratron tubes is conducting, and, 
when it is off on the other side, the other tube 
is conducting. The outputs of these thyratron 
tubes energize the coils of electromagnetic 
clutches. 

The manner in which the thyratron outputs 
control the position of the sensitive head is in¬ 
dicated schematically in Figure 14. This figure 
does not correspond with the actual mechanical 


wards the correct E-W position. However, since 
the response of the mechanism is not instan¬ 
taneous, the rotation will overshoot the E-W 
position where the output voltage is zero, so 
that the other thyratron tube is activated (and 
the first is deactivated because the arrange¬ 
ment of the motor-driven contact is such that 
both tubes cannot be conducting at the same 
time). Clutch coil S is energized and a mechani¬ 
cal connection is made through the associated 
clutch disks so that now the flexible shaft is 
rotated in the opposite direction. Thus the 
mechanism is such that the sensitive element is 


FLEXIBLE SHAFT 

WF" 


MAGNETIC 

CLUTCH 



AMPLIFIER WIT 
MOTOR-DRIVEN SWITCHES 


Figure 14. Principle of servo mechanism for inductor compass. 


arrangement used but is intended only to indi¬ 
cate the general principles of the mechanical 
coupling by means of which the servomecha¬ 
nism operates. 

Let us assume that, when the east-pointing 
end of the sensitive element is off towards the 
north from its normal position perpendicular to 
the magnetic meridian, the phasing of the out¬ 
put is such that the thyratron tube connected 
to the clutch coil N (Figure 14) is active. Then 
the rotation of the gears is such that, when the 
mechanical connection is made through the 
clutch disks under coil N, the flexible shaft is 
turned in a direction which will rotate the east 
end of the coil towards the south or back to- 


always turned back towards an E-W position 
and hunts about that position. This is the re¬ 
quirement for driving the azimuth element of 
the odograph so that, if a connection is made 
from the output gearing (through another 
flexible shaft) such that the position of this 
shaft bears a fixed relation to the shaft con¬ 
trolling the orientation of the sensitive head, 
and therefore to the magnetic meridian, it can 
be used to control the azimuth element in the 
odograph. 

Figure 15 shows the sensitive head as hung 
on gimbals with the damping vanes. The entire 
suspended assembly hangs in a small tank of 
kerosene. 





















20 


COMPASSES AND ODOGRAPHS 


Figure 16 shows the sensitive head as de¬ 
veloped for mounting in the standard compass 
case. 

Performance Tests 

A very extensive series of performance 
tests 24 was made of the inductor compass con¬ 
nected with the standard IBM vehicular odo- 






Figure 15. Photographs of sensitive head of in¬ 
ductor compass, showing suspending gimbals and 
damping vanes. 

graph (ratchet drive) on a V^-ton 4x4 truck 
and on a M3A1 light tank. Comparative runs 
were made at low, medium, and high speeds 
with the inductor compass, the standard M-l 
compass, and the improved DTM compass pre¬ 
viously described (Section 1.3.4). These tests 
indicated that at low speeds all three compasses 
gave reasonably satisfactory results. At me¬ 
dium speeds, the standard M-l compass began 
to fail and at high speeds and rough travel was 


far from satisfactory. The inductor compass 
and the improved DTM compass both gave 
much better results at high speeds, with the 



Figure 16. Inductor-type compass as developed 
for mounting in standard compass case. Upper, 
cover removed; lower, closed, as in use. 

results from the inductor compass apparently 
somewhat superior (see maps, Figures 17, 18, 
and 19). 

In tests with the light tank, 23 the inductor 


Confidential f 








COMPASSES AND COMPASS COMPENSATION 


21 


compass was mounted in three external posi¬ 
tions at heights of 25 in., 10 in., and 6 in. from 
the armor of the tank. These tests indicated 


in., performance was almost as good as with a 
height of 25 in. and that this performance was 
generally satisfactory, as maps made with the 



Figure 17. Odograph test run in %-ton 4x4 truck (jeep), with inductor compass; 30-35 mph, moderately 
rough roads. 



Figure 18. Odograph test run in jeep, improved DTM compass, 30-35 mph. Same route as Figure 17. 


satisfactory compensation could not be main¬ 
tained when the compass was as close as 6 in. 
from the armor, but that, with a height of 10 


compass in the 10-in. position were consistently 
under 3 per cent in error. Figure 20 shows a 
test run with the inductor compass in the 10-in. 









22 


COMPASSES AND ODOGRAPHS 



Figure 19. Odograph test run in jeep, standard M-l compass, 30-35 mph. Same route as Figure 17. 



Figure 20. Odograph test run in M3A1 light tank. Inductor compass outside tank, 10 in. above armor. 


CONFIDENTIAL J 




























COMPASSES AND COMPASS COMPENSATION 


23 


position, with the roads over which the run was 
actually made traced on the same map. 


The Gyrostabilized Fluxgate 
Compass 

This is a commercial instrument, developed 
by the Pioneer Instrument Company for other 
purposes and is not a part of this OSRD project. 


(each of the three arms of the triangle is, in 
principle, similar to the sensitive element of the 
GM inductor compass). The three windings are 
symmetrical, so that, if no external magnetic 
field traverses the Mu-metal core, the voltage in 
each of the three secondary windings is zero 
and there is no output. If, however, the sensi¬ 
tive element is traversed by a magnetic field, 
voltages are induced in each of the three second¬ 
ary coils, and the magnitude and phase of these 
voltages vary, depending upon the direction of 


AMPLIFIER. 



Figure 21. Schematic drawing of operating principle of fluxgate compass system. 


However, since it became an essential part of 
the airborne applications, a brief explanation of 
its principles is included to show how it oper¬ 
ated and was connected in with equipment de¬ 
veloped by the OSRD to make the complete air¬ 
borne odograph. 

Principles of Operation 

The primary magnetically sensitive element 
of this compass (Figure 21) is a triangular 
frame of high-permeability (Mu-metal) ma¬ 
terial with each of the three sides carrying a 
double primary and single secondary winding 


the magnetic field with respect to the three 
sides of the triangle. Thus, if the assembly is 
held in a horizontal plane, the phase and mag¬ 
nitude of the output voltages in the three-phase 
system are dependent upon the direction of the 
horizontal component of the earth’s magnetic 
field with respect to the three coils. 

The magnetically responsive fluxgate unit is 
held in a horizontal position by a specially con¬ 
structed gyroscope which contains an automatic 
and continuously active erecting device such 
that, at all times, the gyroscope tends to main¬ 
tain a vertical axis so that the magnetically 


riAL f 



























































24 


COMPASSES AND ODOGRAPHS 


sensitive element is acted upon only by the 
horizontal component of the earth’s magnetic 
field. The output of the fluxgate element is con¬ 
nected by means of a servomechanism (operat¬ 
ing on the autosyn principle) to a master indi¬ 
cator, the pointer of which is driven by a small, 
two-phase, low-inertia motor, one phase of 
which is excited by the amplified output of the 
autosyn rotor. The motor is mechanically con¬ 
nected to the rotor in such a way that it tends 
to turn it back to the position of zero output, 
when the excitation of one phase of the motor 
field drops to zero and the motor stops. This 
action serves to maintain a fixed relation be¬ 
tween the pointer and the output from the flux- 
gate element such that the direction of the 
pointer corresponds with the direction of the 
magnetic field through the fluxgate coils. The 
master indicator motor also controls the posi¬ 
tion of the rotor of a magnesyn to which an¬ 
other magnesyn at another location can be con¬ 
nected, thus serving as a repeater by which the 
position of the master indicator can be shown 
at one or more other locations. As described in 
the section on the airborne odograph (Section 
1.5.4), there is an autosyn within the integra¬ 
tor, connected to the master indicator, which 
controls a servomechanism driving the direc¬ 
tion elements of the integrator. 

The fluxgate compass system contains within 
its master indicator an arrangement by which 
compensation for inaccuracies in compass indi¬ 
cation can be made mechanically. This is done 
by a series of screws at 15-degree intervals in 
a ring around the indicator. By adjusting these 
screws, the form of a cam surface is adjusted, 
and a follower on this surface modifies the 
coupling between the primary direction element 
and the indicator in such a way that ordinary 
deviations of the compass from its correct indi¬ 
cation can be compensated. For this reason, it is 
not necessary ordinarily to make adjustments 
of the magnetic environment of the compass 
element itself to take care of fixed or induced 
fields, but their effect in disturbing the compass 
indication is taken care of at the master indi¬ 
cator by adjustment of the compensation ring. 

Performance tests of several airborne odo¬ 
graph units connected with the gyrostabilized 
fluxgate compass are included in Section 1.6. 


14 TRUE MILEAGE AND SPEED 
DEVICES 

141 Introduction 

When making odograph installations in air¬ 
craft or on boats, it is necessary to provide an 
accurate log (distance) or speed unit which will 
take the place of the speedometer shaft used for 
the distance element in land vehicle installa¬ 
tions. For air- and water-driven devices, no ap¬ 
preciable power can be drawn from the primary 
element actuated by motion through the air or 
water, as any drag would affect the speed or 
distance indication. Therefore, all air or marine 
logs or speedometers require some sort of fol¬ 
lower or servomechanism from which power to 
operate the odograph may be drawn. 

Some of the devices described in this section 
were developed entirely outside the odograph 
project but were adopted as essential parts, par¬ 
ticularly of airborne installations. The descrip¬ 
tions of such devices included herein are brief 
and are intended only to indicate their prin¬ 
ciples and methods of operation so as to clarify 
their function in the installations of which they 
became essential parts. 


True Air Mileage Devices 

Various types of air mileage devices have 
been considered in connection with the airborne 
odograph. The usual airspeed indicator as used 
on airplanes uses a pitot tube which operates on 
the difference between the pressure in a tube 
opening forward into the airstream and the 
static air pressure. This pressure difference, 
and consequently the airspeed indication, is de¬ 
pendent upon the air density as well as on the 
speed of the plane through the air (but this is 
a satisfactory instrument from the pilot’s view¬ 
point because the performance of the plane de¬ 
pends on this indicated airspeed rather than the 
true airspeed). To make a true airspeed indi¬ 
cator, some other device must be used or the 
simple airspeed indications must be corrected 
to take account of the variable density and 
temperature of the air. 




TRUE MILEAGE AND SPEED DEVICES 


25 


The Simple Impeller Log 

This device consists of a fan or blade rotated 
by motion through the air so that the impeller 
acts like a screw, and the amount of rotation is 
directly proportional to the distance moved. Of 
course, no power can be drawn from the rotat¬ 
ing member itself, but it is possible to actuate 
electric contacts or other electric controls in 
such a way that the speed of a motor or other 
parts from which power can be drawn is regu¬ 
lated by the rate of rotation of the impeller. 
Extensive tests of such a device 17 indicated that 
it is quite satisfactory for moderate airspeeds, 
such as are encountered in lighter-than-air 
craft, but that it encounters serious difficulties 
due to air drag for very high speeds, such as are 
met in modern planes. 

The Schwien True Airspeed Meter 

This instrument b is a modified pitot tube- 
type airspeed indicator which contains a system 
of levers and pressure- and temperature-respon¬ 
sive elements so arranged that corrections for 
air density and temperature are automatically 
made and the indicator shows true airspeed 
rather than pitot tube pressure. This instru¬ 
ment was originally designed as an indicator 
only. In order to apply it to the odograph, a 
pickup was made by arranging a potentiometer 
around the face of the instrument. 111 A motor- 
driven contact element is mechanically moved 
in and out at short time intervals, so that the 
indicator pointer serves as the movable contact 
on the potentiometer, and the voltage between 
this contact and one end of the potentiometer is 
proportional to the true airspeed. By means of 
electronic circuits and a servomechanism, this 
voltage is balanced with that of a similar po¬ 
tentiometer in the odograph integrator, and the 
position of this balance controls the speed of 
drive of the indicator disks so that this speed 
is proportional to the true airspeed. 

The British Air Mileage Unit 

In this instrument, 0 the pitot tube pressure is 
balanced against pressure supplied by a motor- 

b This device was not developed as part of the odo¬ 
graph project but was modified somewhat and used in 
some of the earlier airborne odograph installations. 

C Not developed as part of this odograph project but 
used for many airborne installations. 


driven blower. The pitot tube pressure acts on 
one side of a diaphragm, and the pressure from 
the motor-driven blower acts on the other side. 
The air input to the blower is taken from out¬ 
side the ship, and also an arrangement is made 
so that this air is swept over the fan and other 
parts of the device. Thus the temperature and 
pressure of the air operated on by the blower 
are the same as those of the air which gives the 
pitot tube pressure. Then the pitot tube pres¬ 
sure on one side of the diaphragm and the pres¬ 
sure from the blower air on the other side are 
subject to the same laws of variation with tem¬ 
perature and pressure, and, consequently, the 
speed of the blower required to furnish the 
same pressure as that given by the pitot tube 
is directly proportional to the airspeed. Thus, 
if a servomechanism is arranged to regulate 
the motor speed so that the diaphragm is kept 
balanced, this speed will be directly propor¬ 
tional to the airspeed of the plane, and the 
blower motor can be connected directly to the 
speed unit of the odograph. Certain adjust¬ 
ments in the operating position and a spring 
bias on the diaphragm are provided to correct 
for systematic discrepancies in performance, 
and the setting of these adjustments is made in 
calibrating the device. 

The Pioneer Pump Unit 

This device d is similar in general principle to 
the British air mileage unit except that in this 
device the pitot tube pressure and pump pres¬ 
sure operate on separate diaphragms which are 
connected by a linkage unit. This unit controls 
circuits governing the motor speed and pro¬ 
vides adjustments for making corrections for 
certain systematic inaccuracies. 


1,4,s Comparison of Airspeed Meters 
for Odograph Installations 

Calibrations and comparative tests indicated 
that both the Schwien true airspeed indicator 
and the British air mileage unit gave fairly 
satisfactory results and came within 1 or 2 per 
cent of correct airspeeds in ranges from about 

d Not developed as part of the odograph project but 
used in some aircraft installations. 


: I 







26 


COMPASSES AND ODOGRAPHS 


60 to 300 mph. Since the pitot tube pressure is 
proportional to the square of the speed, devices 
of this kind are inherently unsuited to a wide 
speed range and become poor in the lower 
ranges. The overall performance of the Pioneer 
unit was somewhat less satisfactory than that 
of the British unit. From the standpoint of di¬ 
rect applicability, the British and Pioneer units 
are parallel in that they each have a motor 
which rotates at a rate proportional to airspeed 
and this motor can be connected directly to the 
odograph. The Schwien instrument is somewhat 
simpler in its operation but requires an addi¬ 
tional unit (the potentiometer and associated 
electronic controls) to permit operation of an 


through the water. The water log as developed 
for the odograph application 18 uses a screw 
(like a small propeller) driven by motion 
through the water together with a servomech¬ 
anism by which a motor is controlled to rotate 
at a rate proportional to that of the screw with¬ 
out drawing enough power from the screw to 
affect its rate of rotation. 

A rather difficult problem arises in finding 
a suitable position for the screw both from the 
standpoint of damage to the screw, which may 
result by striking bottom or docks, as when 
landing, and from the standpoint of eddies and 
cavitation, which would affect its indication. 
Some work was done in developing a retractable 


Table 1. Comparative summary of airspeed devices. 


Item 


Schwien 


Unit 

British 


Pioneer 


Average error in flight (per cent) 
Reliability 

Calibration and compensation 
Range (knots) 

Voltage requirements (volts) 
Approximate weight exclusive of 
cables and connections (lb) 
Installation 

Vibration 

Temperature compensatidn 
Adaptability to odograph as re¬ 
gards integrator 

Availability 


113 
Good Good Poor 

None possible Laboratory calibration necessary 

50-300 60-300 100-480 

None 24-28 dc 24-28 dc 

26 or 115, 400-c 

2 17 10 


Easy, location Position critical with respect 

not critical to skin of ship 

Not seriously affected Critical to operation 

Rapid, accurate Slow in response 


Additional components Readily adaptable to fundamental design 

needed complicate design 

No production Extensive production 


odograph. For this reason, and also because the 
British air mileage units were available while 
a Schwien unit was not so readily available, the 
British unit was used for most airborne odo¬ 
graph installations. A general comparison of 
the various airspeed units and their applica¬ 
bility to odograph installations is shown by 
Table l. 17a The reasons for the adoption of the 
British unit for most aircraft odograph instal¬ 
lations are evident from the factors indicated 
by this table. 


144 Sea Logs 

In using an odograph on boats, the problem 
arises of devising a suitable device to give the 
distance traveled or rate of travel of the boat 


screw which would be released by a trigger 
mechanism with the trigger ahead of the screw, 
so that it would be pulled quickly out of the way 
when the trigger is struck, thus preventing 
damage by striking an underwater object. This 
was fairly successful for low and moderate 
speeds but was difficult for application to high¬ 
speed boats because of the short time available 
for clearance after the trigger is actuated and 
the disturbance to the stream lines caused by 
the trigger mechanism itself. 

The problem of suitably locating a water log 
was a special one for each craft to which the 
odograph was fitted. 

Servomechanisms 

Ratchet Motor. One of the most useful of the 
servomechanisms used to give an indication 


CONFIDENTIAL j 












ODOGRAPH INTEGRATORS 


27 


proportional to the rate of rotation of the screw 
was a ratchet motor controlled by electric con¬ 
tacts driven by the log unit. 1 ® Contacts operated 
by the ratchet motor controlled another motor 
from which power could be taken to drive the 
odograph. 

Frequency Meter. Another development with¬ 
in this general project was that of a marine 
speedometer which was designed primarily as 
a speed indicator rather than as a part of an 
odograph installation. A simple electric circuit 
for this purpose uses a saturated transformer 
in which the induction in the secondary is pro¬ 
portional to the frequency of interruption of 
the primary current. 10 A relay which is oper¬ 
ated at a frequency controlled by a contactor on 
the rotating screw carries contacts which inter¬ 
rupt the primary of the transformer and also 
rectify the secondary output so that a simple 
direct-current meter has a deflection propor¬ 
tional to the speed of rotation of the screw. 

Variable-Frequency Synchronous Motor Sys¬ 
tem. 111 A rather elegant system, developed to the 
experimental stage, was that using a two-phase 
generator and motor. The generator rotor, 
turned by an impeller in the fluid stream, gen¬ 
erates very low-power, two-phase current at a 
frequency proportional to the rate of rotation. 
Each phase is amplified separately (to a power 
output of about 25 watts), and these outputs 
are supplied to a two-phase motor to drive the 
odograph or other apparatus. 

The electrical complications and the com¬ 
paratively large weight and power require¬ 
ments prevented any extensive applications of 
this system. 


i-s ODOGRAPH INTEGRATORS 

151 General Requirements of 

Odograph Integrators 

Before describing the mechanical parts and 
operations of the several integrators which 
were developed, it will be useful to review the 
general requirements and functions which are 
common to all of them. 

The integrator must take as its input either 
distance or speed and direction and must give 


as its output the distance traveled resolved into 
cardinal components, so that the sums of all mo¬ 
tions of the vehicle parallel to the reference di¬ 
rection and perpendicular to that direction are 
continuously shown. This means that each of 
these components of motion must operate one 
of a pair of elements within the integrator 
which is moved or turned by increments which, 
at all times, are proportional to the increments 
of travel parallel to the reference direction 
(normally N-S) and perpendicular to the ref¬ 
erence direction (normally E-W) ; i.e., the 
increments must be added up as As cos a and 
As sin a, where As is the increment of dis¬ 
tance and a is the angle between the instan¬ 
taneous direction of motion and the refer¬ 
ence direction. This means that some sort of 
continuously variable coupling must be used to 
provide the varying degree by which each ele¬ 
ment of motion of the vehicle is projected onto 
the reference axes. The motion or turning of 
mechanical elements satisfying these conditions 
may be caused to actuate counters by which the 
increments of N-S and E-W components of the 
motion of the vehicle are added from the initial 
starting point so that each of the two horizontal 
coordinates of instantaneous position is con¬ 
tinuously indicated. Also, the same increments 
can be transferred to two perpendicular screws 
controlling the motion of a pencil or marking 
device so that one screw gives the N-S position 
and the other the E-W position. Then the posi¬ 
tion of the pencil on the marking table corre¬ 
sponds, at all times, to the position of the ve¬ 
hicle on the ground. If the plotting table over 
which the pencil moves carries a map and the 
scale of the motion of the pencil is properly 
adjusted to the scale of the map on the table, 
the motion of the pencil will trace a line on the 
map which corresponds to the course traveled 
by the vehicle over the ground. 

The Scotch Yoke 

A simple mechanical principle which serves 
to give motions proportional to sin a (or cos a) 
is the Scotch Yoke, and it or its equivalent is 
used in each of the three integrators described 
in this section. The principle of the Scotch 
Yoke, as shown in Figure 22, consists essen¬ 
tially of a disk carrying a pin or roller which 


CONFIDENTIAL 







28 


COMPASSES AND ODOGRAPHS 


slides or rolls within the slot of the yoke. This 
slot has a fixed azimuth or direction and is long 
enough to permit the pin to travel back and 
forth in the slot so that the motion of the yoke 
corresponds to the projection of the motion of 
the pin (or roller) onto a diameter perpendicu¬ 
lar to the direction of the slot. 

It is evident that the position of the bar car¬ 
ried by the yoke is directly proportional to the 
sine of the angular position of the disk carry¬ 
ing the pin (which is referred to as the sine 


SIN-DISK 



Figure 22. Schematic diagram showing princi¬ 
ple of Scotch Yoke. 

disk). If there is a second pin on the other side 
of the disk (as shown in the figure) or on a 
separate disk but at an angle of 90 degrees with 
the first and operating in a similar Scotch Yoke, 
it is evident that this second Scotch Yoke will 
have a position proportional to the cosine of the 
angle of the sine disk. If means are provided by 
which the rotary motion of the odograph ele¬ 
ment is variably coupled to driven elements 
with the degree of coupling proportional to the 
positions of the Scotch Yokes, Y x and Y„, Figure 
22, the motion of the driven elements will then 
be proportional to the amount of travel of the 
vehicle multiplied by the sine and by the cosine 
of the angle of the sine disk or disks carrying 
the pins. If the position of the sine disk is con¬ 
trolled by the compass, then the requirement 
that the motion of the driven element is pro¬ 
portional to the motion of the vehicle times the 
sine (or cosine) of the angle of heading will be 
fulfilled. 


Any mechanical or electrical principle which 
provides that the degree of coupling between a 
driving and a driven unit is proportional to a 
linear displacement, such as is provided by the 
bar of a Scotch Yoke, could be made the basis 
of an integrating unit. Several such principles 
have been applied in various machines and in¬ 
struments. Some of these use a frictional cou¬ 
pling between a fixed driving member and a mov¬ 
able driven member, the position of which, with 
respect to the driving member, is varied. Others 
use a positive drive through gears or ratchets. 
It is evident that, in odograph applications, it is 
essential that careful consideration be given to 
the effect which violent motion or shock might 
have on the mechanical elements involved, and 
that preference be given to positive drive units 
over those using friction drives when conditions 
are very severe, such as on rough-riding land 
vehicles, particularly tanks, but that a friction 
drive device might be satisfactory under less 
severe operating circumstances, such as air¬ 
craft or boat applications. 


i. a .2 'j'jjg DTM Experimental Integrator 

The original model of this integrator was de¬ 
veloped by the Department of Terrestrial Mag¬ 
netism of the Carnegie Institution of Washing¬ 
ton and was built up largely from parts and 
gears of Monroe calculating machines. The ex¬ 
perimental model was taken over later by the 
Monroe Company and redesigned and engi¬ 
neered for quantity manufacture. 

The Stepped Tooth Gear 
Variable Coupling 

The essential variable coupling element of 
this integrator is a pair of gears with stepped 
teeth, Figure 23. The length of the teeth along 
the face of the gears varies from a very short 
tooth to a tooth running entirely across the gear 
face, the ends of the teeth forming a one-turn 
spiral (also see Figure 10). The two similar 
gears are rotated in opposite directions by gears 
connected directly to the odometer element 
(speedometer cable). Each of these gears en¬ 
gages a driven gear which is moved parallel to 
the axis of the driving gears by a Scotch Yoke. 


CONFIDENTIAL J 
























ODOGRAPH INTEGRATORS 


29 


It is evident that, if this driven gear is in the 
space between the two driving gears, it will not 
be turned. If it is a little to one side, it will be 
engaged by only the one longest tooth and will 
be rotated only one tooth for each revolution of 
the driving gear. As it is moved farther and 
farther toward the outside edge of the driving 
gear, the driven gear will be engaged by more 
and more teeth of the driving gear until, when 
it is at the extreme outer edge, it will be en¬ 
gaged by teeth all the way around and will be 



Figure 23. Schematic drawing showing operat¬ 
ing principle of stepped-tooth gear integrator. 


rotated by a maximum amount. If the driven 
gear crosses the central space between the two 
and begins to be engaged by the oppositely ro¬ 
tating driving gear, it is evident that a similar 
coupling will take place, but with the driven 
gear rotating in the opposite direction. Thus the 
amount of rotation of the driven gear will be 
directly proportional to its position along the 
axis of the stepped driving gears, and the con¬ 
dition that its rotation is proportional to the 
sine of the angle of heading will be fulfilled, as 
the position is controlled by the sine disk 
slaved to the compass. The second driven gear 


engaging the same driving gears and controlled 
by a second Scotch Yoke gives motion which is 
proportional to the cosine of the angle of head¬ 
ing. Each of the two driven gears turns a 
splined shaft which is geared to one or the other 
of the two lead screws giving the two coordi¬ 
nates of motion to the mapping pencil, so that 
the motion of these two screws is proportional 
to the forward motion of the vehicle multiplied 
respectively by the sine and cosine of the angle 
of heading and, therefore, the condition for 
mapping is fulfilled. 

Interpolation by Hunting 

It is evident that the degree of coupling be¬ 
tween the driving and driven gears varies by 
discrete steps, as the lateral motion of the 
driven gear picks up or drops one tooth of the 
driving gear. However, on account of the oscil¬ 
lation of the compass follower, the Scotch Yoke 
continually moves back and forth by a small 
amount. If its mean position is such that the 
driven gear is intermediate between the ends of 
two teeth on the driving gear, this motion back 
and forth is such that part of the time a given 
number of teeth is engaged, and part of the time 
one more tooth is engaged. This oscillation 
serves to accurately interpolate between the in¬ 
tegral number of teeth of the driving gear, so 
that the average rotation of the driven gear is 
proportional to the whole number of teeth plus 
a fractional number to give the proper fraction 
so that the correct rotation of the driven gear 
results. The analysis of this interpolation and 
a theory of linear hunting have been worked 
out in considerable detail. 15d 

Auxiliary Indications 

As now developed, two other indications be¬ 
sides the map itself are shown on the visible 
face of the machine. One of these is a dial or 
azimuth indicator which repeats the reading of 
the compass and, therefore, gives a continual 
indication of the heading of the vehicle. This is 
desirable as the compass itself is usually in an¬ 
other part of the vehicle with its position dic¬ 
tated by considerations of magnetic environ¬ 
ment, and is totally enclosed so that the position 
of its card is not visible. 

The second auxiliary indication carried by 















30 


COMPASSES AND ODOGRAPHS 


the integrator unit is a pair of counter dials 
which add up the two components of motion. 
These can be calibrated in miles or other units 
to give the total distance north or south and 
east or west of the starting point at which they 
are set at zero, or can be calibrated and set to 
give latitude and longitude. A third dial may be 
used to give the total distance traveled by the 
vehicle. 

Provisions for Variable Map Scale 

It is evident that the scale of the map pro¬ 
duced, i.e., the ratio of the motion of the pencil 



MOVABLE SHIELDS 

Figure 24. Schematic diagram showing princi¬ 
ple of pawl-and-ratchet variable coupling. 

on the map to the motion of the vehicle on the 
ground, will depend upon the various gear 
ratios of the odometer drive and of the coupling 
between the driven gears and the lead screws. 
For different applications of the odograph, it is 
desirable to make maps at different scales, 
which requires that the operator be able to 
change the scale ratio for different circum¬ 
stances. For instance, if a map were desired of 
a short operation extending only a few miles 
from the starting point, it might be desirable 
to use a scale of, say, 1 to 24,000 (approxi¬ 
mately 2!/2 in. equal 1 mile), which would per¬ 


mit mapping the proposed operation on a rela¬ 
tively open scale on the limited area of the odo¬ 
graph mapping table. For a more extended op¬ 
eration, a map covering a much larger area, 
and therefore with a greater scale ratio, would 
be desirable. To permit a variable scale ratio, a 
set of gears is provided so that the coupling 
ratio between the odometer drive and the inte¬ 
grator may be varied. 

In the DTM model integrator, as engineered 
for manufacture, the ratio-changing gears are 
much like a miniature of the variable speed 
transmission of an automobile. By setting a dial 
controlling the positions of these gears, the odo¬ 
graph map will be drawn according to the 
selected one of a group of ratios corresponding 
to commonly used mapping scales. Moreover, an 
interpolating device is included which has a 
variable coupling (using stepped gears similar 
to those used for the integrator itself) by which 
a wide range of scale ratios may be interpolated 
between those of the primary scale ratio selec¬ 
tor. 

153 The IBM Ratchet Drive Integrator 

This is an alternative integrator which was 
used on many land vehicle odograph installa¬ 
tions and was made in some quantity. The de¬ 
vice was developed and manufactured by the 
International Business Machines Corporation 
under a contract with OSRD. In the following 
paragraphs, the essential functions performed 
by this integrator will be described without 
going into all the mechanical details which, in 
the aggregate, involve an assembly of gears, 
ratchets, clutches, etc., with the individual parts 
being rather similar to those of calculating and 
other business machines. 27 

The Ratchet Drive Variable Coupling 

The variable coupling for this integrator is 
attained through the use of ratchets and pawls, 
together with a set of rotatable shields so ar¬ 
ranged that an opening between the shields per¬ 
mitting the engagement of the pawl on the 
ratchet is variable, and this opening is con¬ 
trolled by the position of a Scotch Yoke. The 
general principle of this arrangement is shown 
in Figure 24. 


CONFIDENTIAL 

















ODOGRAPH INTEGRATORS 


31 


The driving wheel carrying four pawls is 
connected to the odometer element and rotates 
by an amount proportional to the travel of the 
vehicle. As this wheel rotates, the pawls engage 
the ratchet for that part of the rotation during 
which they are allowed to drop down into the 
gap between the stationary and movable shields. 
Thus the amount of motion which is trans¬ 
ferred from the driving pawls to the driven 
ratchet is governed by the opening of the 
shields. It is evident that by making this open¬ 
ing directly proportional to the position of the 


It is evident that the pawl-and-ratchet cou¬ 
pling between driving and driven members can 
give only a discrete number of changes in the 
ratio of coupling, for it is governed by the dis¬ 
crete number of ratchet teeth which are ex¬ 
posed by a variation from zero to maximum of 
the shield opening, corresponding to a rotation 
of 90 degrees of the sine disk. In this integrator, 
the number of teeth is twenty-nine, so that only 
twenty-nine coupling steps are available. How¬ 
ever, the 10-degree hunting of the compass fol¬ 
lower, which was mentioned in the section on 



Figure 25. Map scale-changing unit, IBM integrator. 


bar of a Scotch Yoke, as shown by Figure 24, 
the amount of motion transferred to the driven 
ratchet will be that of the wheel carrying the 
driving pawls multiplied by the sine (or cosine) 
of the angle of the sine disk. A set of block-out 
shields (not indicated in the figure) is used to 
transfer the driving effect of the pawls from 
one ratchet to another when the Scotch Yoke 
passes through its zero or middle position. The 
second ratchet is connected through reverse 
gearing so that the output drive is reversed, 
thus giving the required change of sign when 
the component of motion changes from north to 
south. 


compasses, provides accurate interpolation be¬ 
tween the discrete ratchet tooth intervals. As 
the compass follower swings back and forth 
through its 10-degree arc, the sine disk con¬ 
trolling the Scotch Yoke also swings through 
this same interval, resulting in a small oscillat¬ 
ing motion of the bars controlling the openings 
of the ratchet shields. Thus, on one revolution 
of the driving wheel carrying the pawls, a pawl 
might engage, say, twenty-three teeth, and on 
the next revolution it might engage, say, 
twenty-two, so that, on the average, the motion 
of the driven ratchet would correspond to 
twenty-two and one-half teeth. It may be re- 









32 


COMPASSES AND ODOGRAPHS 


peated here that the random relation between 
the oscillation of the sine disk and Scotch Yoke, 
which follows the swing of the compass fol¬ 
lower, and the motion of the pawls works out 
in the same way as was mentioned in connection 
with the stepped gear integrator, and that the 
precision of the interpolation between the inte¬ 
gral ratchet steps is entirely adequate for odo- 
graph applications. 1511 

The above description has outlined the means 
by which ratchets are driven by amounts pro¬ 
portional to the motion of the vehicle multiplied 
by the sine (or cosine) of the azimuth of its mo¬ 
tion with respect to a reference (north) direc¬ 
tion. In the actual instrument, there are two 
sets of pawls on opposite sides of the main drive 
gear; one set of pawls and ratchets is controlled 
by a Scotch Yoke, the position of which is pro¬ 
portional to the sine of the azimuth angle, and 
the second set by a second Scotch Yoke, the posi¬ 
tion of which is proportional to the cosine of the 
azimuth angle. The driven elements of these 
two sets are connected through a scale-changing 
gear box to two lead screws. One of these moves 
a carriage in a north-south direction on the odo- 
graph map table. The second lead screw, trans¬ 
verse to the first, is carried on the carriage and 
moves the marking pencil in an east-west direc¬ 
tion. Thus the combination of motion of the two 
screws serves to drive the pencil on the map by 
an amount which is proportional to the cardinal 
components of the motion of the vehicle, and 
thereby reproduces, to scale, the course over 
which the vehicle has moved. 

Scale Changing and Other Accessories 

This IBM integrator has a flexible map-scale 
ratio-changing device which provides not only 
for discrete changes in ratio to correspond with 
certain fixed or standard scales, but also pro¬ 
vides for continuous variation of scale between 
the fixed values. This has been done so that an 
air photograph, for instance, with a nonstand¬ 
ard scale (determined by the height from which 
the picture was made) may be put on the odo- 
graph map table, and the odograph scale ratio 
may be adjusted so that the trace of the course 
followed will fit the air photograph. The dis¬ 
crete scale changes are given by a four-step, 
gear-shifting device, and the continuous varia¬ 


tion is given by a ratchet-and-pawl arrange¬ 
ment similar to that of the primary integrator 
(Figure 25). This gear-and-ratchet assembly is 
interposed between the odometer drive and the 
integrator drive so that it permits changing the 
scale ratio by small steps over a wide range. 

This integrator also contains an azimuth or 
heading indicator which repeats the compass 
bearing by means of a connection between the 
sine disk of the integrator and a pointer of the 
integrator table, which shows the bearing of the 
vehicle with respect to the reference direction. 



Figure 26. Integrator unit of IBM integrator, 
showing Scotch Yoke, part of main driving gear, 
and lock-out shield. 

Furthermore, provision is made through dif¬ 
ferential gears for correction of magnetic devi¬ 
ation so that the indicator continually points to 
the bearing of the vehicle with respect to true 
north, rather than magnetic north. 

This integrator also contains a counter unit 
which provides numerical indications of the 
total miles traveled, and also of the north-south 
and east-west components of the mileage. Pho¬ 
tographs of the complete instrument are shown 
in Figures 26, 27, and 28. 

It should be pointed out that the complexity, 
size, and weight of this and the other integra¬ 
tors described are very materially increased by 
the various auxiliary parts, including the azi¬ 
muth indicator and counters and, particularly, 
by the scale-changing unit. A simple odograph 


CONFIDENTIAL m \ 
















ODOGRAPH INTEGRATORS 


33 


or map-maker at one scale could be a much 
simpler, smaller, and lighter device. 


The IBM Disk Drive Airborne 
Integrator 

The description that follows is based pri¬ 
marily on the Model AO-3 airborne odograph as 
developed by International Business Machines 


receiving autosyn of the odograph integrator, 
there is induced a single-phase output voltage, 
the magnitude and sign of which depend upon the 
rotor position. This voltage passes through zero, 
and the phase reverses when the rotor passes 
through the position which corresponds with that 
of the rotor in the transmitting autosyn of the 
master indicator of the compass. The output of 
the rotor of the autosyn in the integrator controls 
the grids of two thyratron tubes which, in turn, 



Figure 27. General view of IBM integrator with case open. 


Corporation. 20 The reference direction is de¬ 
rived from the Pioneer fluxgate compass sys¬ 
tem, and the distance is taken from a British 
or Pioneer air mileage unit. 

General Description — 

Air Position Components 

A constant-speed motor, 1 (see Figure 29), 
is connected by gears and a clutch mechanism 
and through a differential, 2, to a worm gear 
which drives the rotor of the autosyn, 3, within 
the integrator. The orientation of the three- 
phase field in the autosyn is controlled by the 
transmitting autosyn in the master indicator of 
the fluxgate compass. Within the rotor of the 


control the clutches, 4, which operate the gear¬ 
ing by which the motor turns the autosyn rotor. 
The phase of the control grid voltage of the 
thyratron tubes with respect to that of the plate 
voltage is such that only one tube and one clutch 
can be active at the same time, and the relations 
between the clutches and the gearing are such 
that the autosyn rotor is turned in the direction 
towards that in which the rotor output is zero. 
This serves to keep its orientation the same as 
that of the rotor of the transmitting autosyn in 
the master indicator. The action of the thyra¬ 
tron tubes and the clutches is such that the 
rotor tends to overshoot the zero position, 
whereby the direction of rotation is immedi- 





34 


COMPASSES AND ODOGRAPHS 


ately reversed so that the rotor hunts about the 
zero position. The rate of hunt is controlled 
manually by an external knob (located on the 
course control amplifier) which controls the 
bias voltage on one of the grids of the clutch 
control tubes. 

It was mentioned that the connection to the 
autosyn rotor is through the differential, 2. The 
other side of this differential is connected 



Figure 28. General view of integrator plotting 
table, showing transverse lead screw, direction 
indication, and distance dials. 


through a gear to a control knob, 5, on the front 
of the integrator. Rotation of the differential 
gear by this knob changes the angular relation 
between the clutch control gears and the auto¬ 
syn rotor, thus providing means by which the 
magnetic variation (deviation from true north) 
may be set off. Then the autosyn rotor is bal¬ 
anced at a point corresponding to the magnetic 
north while the gearing connected to the 
clutches hunts about a position corresponding 
to the astronomic north. 

The gearing controlled by the compass drives 
azimuth gears 6E and 6N. Pins, 7, in these 
gears operate in long vertical slots in the slide 


assemblies, 8, moving these slides horizontally 
to positions corresponding to the sine and 
cosine, respectively, of the angle of heading, 
thus acting as Scotch Yokes. The slide assem¬ 
blies control the position of small pickup rollers, 
9N, 9E, which are moved along horizontal di¬ 
ameters over the two Neoprene-covered faces 
of the rotating disk. Thus the speed of rotation 
of these rollers is proportional to their distance 
out from the center of the disk. The rotating 
disk is supported and driven from its periphery 
so that both faces are free and one roller, con¬ 
trolled by one slide assembly, rides on one face, 
and the second roller, controlled by the second 
slide assembly, the pin of which is 90 degrees 
out of phase with that of the first, rides on the 
other face. The disk is driven by gear 11, which 
is connected by a flexible shaft to the motor of 
an air mileage unit, 12, so that the rate of rota¬ 
tion of the disk is directly proportional to the 
speed of the plane through the air. Since the 
azimuth gears and slide assemblies are continu¬ 
ally controlled by the gearing and clutches 
which follow the autosyn rotor, the horizontal 
positions of the two pickup rollers are main¬ 
tained proportional to the sine and cosine of the 
azimuth or heading of the ship. Since the speed 
of rotation of the disk is proportional to the 
speed of the ship, the shafts, 13N and 13E, 
turned by the rollers rotate at speeds propor¬ 
tional to V a sin a and V a cos a, respectively 
(where V a equals airspeed and a equals angle of 
heading). 

The shafts, 13N, 13E, operate pairs of count¬ 
ers, 14N, 14E, which give numerically the north 
or south distance in air miles and the east or 
west distance in air miles. These shafts also are 
connected to one side of differentials, 15N, 15E, 
the input to the other side of which comes from 
the air drift compensator to be described below. 

The Wind Correction Components 

In order to give the position of the plane rela¬ 
tive to the ground, it is necessary to make a 
correction for the magnitude and direction of 
the drift with the wind. Since all the elements 
described above are referred to the air, they 
give the position of the plane relative to the air. 

The correction for drift is made by another 
integrating unit similar to that just described 


CONFIDENTIAL* 








ODOGRAPH INTEGRATORS 



e 



Figure 29. Schematic drawing of disk-drive integrator with wind correction for airborne odograph. 





















































































































































































































































































36 


COMPASSES AND ODOGRAPHS 


except that: (1) the rate of rotation of the sec¬ 
ond integrator disk, 16, is constant as it is 
geared back to the constant speed motor, 1; and 
(2) the radius of pins, 17, in the slide assembly- 
slots, is variable and is controlled by velocity 
cams, 18. When the velocity knob, 19, is turned 
so that the wind velocity indicator, 20, is set on 
a scale at a position corresponding to the actual 
wind, the relative positions of the velocity and 


associated pickup rollers, 25, 25, are set so that 
the two shafts, 26N, 26E, driven by the rollers 
on the two sides of the disk, are turned at rates 
proportional to V w sin (3 and V w cos (3 (where 
V w equals wind velocity, and (3 equals wind 
direction). 

These shafts are connected to the second 
input side of the output differentials, 15N, 15S 
(to which the other input side is connected, as 



Figure 30. Plotting table of airborne odograph showing double threaded lead screws and drive mecha¬ 
nism. 


direction cams are adjusted through the differ¬ 
ential, 21, and are such that the pins, 17, are 
both on a radius out from the center of the disk 
corresponding to the wind velocity. The direc¬ 
tion gears, 22, and velocity cams may be rotated 
together by knob, 23 (through the differential, 
21), which sets the pins corresponding to the 
sine and cosine of the wind direction, as shown 
by the indicator, 24. Then the horizontal posi¬ 
tions of the N-S and E-W slide assemblies and 


previously described, to the output gears of the 
air position integrator disks). The differentials 
serve to combine the two inputs so that the out¬ 
puts of the two differentials which drive the 
two sets of impulse cams, 27N and 27E, are 
V a sin a — V w sin (3 and V a cos a — V„ cos (3, 
respectively. Thus, if correct values of V w and p 
have been set into the wind correction inte¬ 
grator, the wind drift is taken out, and the 
motion of the impulse cams is proportional to 


CONFIDENTIAL 







ODOGRAPH INTEGRATORS 


37 


the cardinal components of the motion of the 
plane with respect to the ground. 

The Plotting Table 

The impulse cams operate electric contacts, 
28N, 28E, which control clutches, N, S, E, W, 
on the plotting table. These clutches control 
gears driven by a motor on the plotting table 
(Figure 30), so that, for each contact of the 



Figure 31. General view of airborne integrator 
and plotting table. 


impulse cams, the corresponding N-S or E-W 
screw on the plotting table is turned by one- 
tenth of a revolution. 

Friction-driven switches, 29N, 29E, change 
the electric connections each time the direction 
of the impulse camshaft reverses, so that the 
impulse is properly transferred to the other of 
the pair of N-S or E-W clutches, and the direc¬ 
tion of rotation of the corresponding screw on 
the plotting table reverses whenever the direc¬ 
tion of motion of the impulse cams is reversed. 

The number of teeth on the impulse cams 
determines the number of contacts per revolu¬ 
tion and thereby determines the rate at which 
the plotting table screws are operated and thus 


the scale at which the stylus traces on the plot¬ 
ting table. Different map scales are made very 
simply by providing impulse cams with differ¬ 
ent numbers of teeth, and the map scale selec¬ 
tor, 30, operates to set the contact to ride on 
the impulse cam having the corresponding num¬ 
ber of teeth. A second plotting table can be 
operated by a second pair of contacts operated 
by the same impulse cams. Furthermore, it is 
not necessary that the two or more contacts be 
operated by the same cam, so that it is possible 
to provide two or more plotting tables operated 
at different scales, if desired. In the instrument 
as built, the scale ratios are in five steps, from 
1 to 40,000 to 1 to 2,000,000. 

The screws on the plotting table are double 
threaded (see Figure 30), and the nut following 
the screws is arranged so that, when it comes to 
the end of travel of either screw, it shifts to the 
other thread and reverses the direction of that 
component of the motion of the stylus. This 
keeps the stylus from running off the edge of 
the table (if the course of the ship would take 
it beyond the limits corresponding to the area 
of the plotting table) by reversing it back onto 
the table in a mirror image of the course which 
it would have if the table were not limited. This 
permits reconstruction of those parts of the 
course which otherwise would not be mapped, 
as they would be beyond the limits of the plot¬ 
ting table. 

The stylus on the plotting table is provided 
with a position marker. When depressed, either 
manually or, if desired, electrically by a push¬ 
button control, the marker makes a small col¬ 
ored inked circle about the point of the marking 
stylus. This provides a simple means by which 
the instantaneous position of the ship may be 
marked at any time on the map. This is particu¬ 
larly desirable in applications where it may be 
necessary to return to a given point or where 
reference to a given spot on the ground may be 
desired. 

Data for Wind Drift Corrections 

The odograph itself provides a means of de¬ 
termining the wind drift for making the wind 
correction. If the plotting table is operated with 
the wind correction at zero, the map will give 
the air position rather than the ground position 







38 


COMPASSES AND ODOGRAPHS 


of the ship. If, at the time the ship is over a cer¬ 
tain point on the ground, a mark is made show¬ 
ing the corresponding position on the odograph 
map and then the ship flies in a loop and comes 
back over the same point on the ground and 
another mark is made on the odograph map, the 
vector connecting these two marks is a direct 


rection controls set accordingly. (See Figure 
48.) Wind correction may be set also directly 
from meteorological observations signaled to 
the plane. 

Pictures and Dimensions of Complete Units 
A general view of the complete integrator 


Figure 32. Interior of airborne integrator. 



measure of the speed and direction of the wind. 
By measuring the azimuth and length of this 
vector and taking proper account of time inter¬ 
val and scale setting, the direction and speed of 
the wind can be determined and the wind cor¬ 


and plotting table is given in Figure 31. An 
interior view is shown in Figure 32, while 
Figure 33 shows the main integrating disk, 
wind correction disk, and slide assemblies. 

The dimensions and weights of the various 



REPORTS ON TEST INSTALLATIONS 


39 


units making up the complete installation of the 
airborne odograph, Type AO-3, and its acces¬ 


sories are as follows: 

Integrator (14%xl4%xl0%i in.) 55 lb 

Plotting table (9iy w x21iM6x3% in.) 15% lb 

Course control amplifier (6%x9%x7 1: J46 in.) 5M> lb 

British air mileage unit 1614 lb 

Fluxgate compass and gyro 7 lb 

Gyro caging motor 2 lb 

Master indicator 614 lb 

Amplifier for compass unit 11 lb 


Total 118% lb 

(Weights are exclusive of connecting cables.) 

16 REPORTS ON TEST INSTALLATIONS 

The general comments of this section are 
based on the various reports which describe spe¬ 


cial test installations, and the pictures and odo¬ 
graph maps are from those reports. Many other 
test runs, not covered specifically by reports, 
were made at various times throughout the de¬ 
velopment. The test installations covered by the 
reports were, in most cases, in relatively early 
stages of particular phases of the development, 
and the maps made suffer from the usual diffi¬ 
culties of early experimental trials. No attempt 
has been made to include results of routine uses 
of the equipment in military operations, as 
records of these are not included in the material 
on which this report is based. 

The test installations mentioned are listed in 
the following table, which includes all tests 
covered by regular reports but no others. 




Test Installations 



Reference 

Vehicle 

Date 

Compass 

Mileage unit 

Integrator 



Vehicula 

r Odograph 



2 

British jeep 

Dec. 1942 

DTM 

Speedometer 

IBM 




(Monroe) 

cable 

(ratchet drive) 

19 

4x4 %-ton jeep 

Oct. 1943 

GM Ind. and 

Speedometer 

IBM 

21 



Monroe 

cable 


lb 

Light tank 

July-Aug. 

DTM 

Speedometer 

Monroe 



1942 


cable 

(stepped gear) 

lc 

Med. tank 

June 1942 

DTM 

Speedometer 

Monroe 





cable 


If 


Jan.1943 

DTM 

Speedometer 

Monroe 





cable 


22 

M3A1 light tank 

July 1944 

GM Ind. 

Speedometer 

Monroe 




outside armor 

cable 


8 

Half-ti-ack 

Jan.-Mar. 

DTM 

Speedometer 

Monroe 



1943 


cable 


5 

M-29 Army 

Nov.-Dec. 

Monroe 

Trailed wheel 

Monroe 


motor sled 

1943 



(marine type) 

4 

T-15 snow tractor 

Jan.-Mar. 

DTM 

Speedometer 

IBM Model B 


(Weasel) 

1943 


cable 

(ratchet drive) 

6 

DUKW 

Dec. 1942 

Monroe 

Speedometer 

IBM 


(amphibious truck) 

Mar. 1943 


and impeller 

(disk drive) 



Mar. 1944 

Monroe 

Monroe log 

IBM 





pickup 

(ratchet drive) 



Airborne 

! Odograph 



Id 

B-18 

Oct. 23 1942 

Fluxgate 

Schwien 

IBM 

le 

Army bomber 

Oct. 9 1942 



(disk drive) 

lh 

B-24 

Feb.1943 

Fluxgate 

Schwien 

IBM 


Army bomber 





9 

RA-29 

Apr. 1943 

Fluxgate 

Pioneer AMU 

IBM 

7 

OAIO 




IBM 


Army patrol 

Nov. 1943 

Fluxgate 

British AMU 


flying boat 

Jan.1944 




8 

PBM 



British AMU 

IBM 

Navy patrol 

Dec. 1943 

Fluxgate 


flying boat 

Jan.1944 










40 


COMPASSES AND ODOGRAPHS 


161 British Jeep 

This test installation was made as a demon¬ 
stration of the odograph when it was taken to 
England in the winter of 1942-1943. The instal¬ 
lation was made in England on a British jeep 



Figure 33. Interior view of airborne integrator, 
showing integrating disk and wind correction 
disk. 


No maps or figures of these tests are repro¬ 
duced. 


14 -Ton, 4x4 Truck (Jeep) 
Comparative Tests of Inductor and 
Standard Compasses' 22 


Two sets of comparative tests of different 
types of compasses were made to show the rela¬ 
tive performance of the IBM inductor compass, 
the standard M-l compass, and the DTM im¬ 
proved compass. The first tests (October 1943) 
were made with an earlier model of the in¬ 
ductor compass, installed in a jeep and con¬ 
nected with the production model IBM plotting 



(of American manufacture), and the installa¬ 
tion was, in general, similar to those made on 
similar vehicles in the United States. 

The purpose of these tests was to demon¬ 
strate the operation of the equipment to in¬ 
terested British Army officers, a number of 
whom observed the operation while making 
small maps; some larger maps were made. In 
general, the operation was considered satisfac¬ 
tory with closures on trips of from 10 miles to 
200 miles generally between 1 and 2(4 per cent. 


Figure 34. Installation of inductor compass on 
jeep, showing iron cylinders for quadrantal com¬ 
pensation. 

unit. The second series of tests (April 1944) 
was made with the modified inductor compass 
(modified to fit into the standard M-l compass 
case). 

In both installations, magnets for semicircu¬ 
lar and heeling compensation were mounted 
within the compass assembly, and two iron 
cylinders, one on each side of the compass, were 

































REPORTS ON TEST INSTALLATIONS 


41 


used for quadrantal compensation. (See Figure 
34.) 

The tests consisted of a series of runs at vari¬ 
ous speeds over a rough course. The purpose of 
varying the speed was primarily to subject the 
installations to various degrees of shock and 
vibration. The original reports contain many 
odograph maps made at various speeds by the 
different installations over the same courses. 
Examples of these maps have been included as 
Figures 13, 14, and 15 in Section 1.3.6. 

These tests showed that both the inductor 
compass and the DTM improved compass were 
far superior in performance to the standard 
M-l compass at medium and high speeds, for 
which the equipment was exposed to severe 
shock and vibration. 

1 - 6 - 3 Light Tank lb 

This installation used a DTM compass and a 
Monroe integrator. The compass was mounted 
within the armor of the tank. The tests were 
conducted to determine the difficulties which 
would have to be met for tank installation. The 
principal difficulties encountered were disturb¬ 
ances to compass compensation caused by 
changes in the magnetic condition of the ve¬ 
hicle, by the change of position of certain mov¬ 
able equipment within the tank, and by electric 
currents. The disturbances were materially re¬ 
duced by replacing an iron gear shift lever by 
one of brass and by rearranging some of the 
heavy current-carrying electric circuits to elim¬ 
inate grounded returns, and thereby reducing 
the area of the circuits and correspondingly 
their magnetic fields and effects on the compass. 

The tests included some 1,300 miles of map¬ 
ping over roads of all sorts, from winding dirt 
roads to paved highways. Some of the maps 
were seriously in error due to compass disturb¬ 
ances, but many quite satisfactory maps were 
obtained when a number of minor mechanical 
and electrical faults in the installation had been 
corrected. One of the better maps from this 
series of tests is shown as Figure 35. 

These tests served to point out a number of 
weaknesses of the equipment, none of which 
were fundamental, and to indicate the nature of 
the problems and the special arrangements of 


equipment and certain minor modifications of 
parts of the tank (particularly electric circuits 
and certain moving iron parts) which would be 
necessary. The overall result seems to indicate 
that, with care in installation and frequent at¬ 
tention to compass compensation, reasonably 
satisfactory compass and odograph operation 
could be expected in a tank. 



Figure 35. Trace of map made in light tank 
with compass inside armor. Double line: actual 
route; solid line: trace made by odograph. 


16 - 4 Medium Tank (M4A1E2) 10 ' lf 

A test installation in a medium tank turned 
out to be more complicated and difficult than 
those in any of the other Army vehicles. The 
difficulties arise because of the serious disturb¬ 
ances to the magnetic compasses due to: (1) 
the heavy steel armor which changes its mag¬ 
netization and also shields the compass to a 
large extent and thereby reduces the strength 
of the controlling magnetic field; (2) electric 
currents from various circuits in the tank 
which produce magnetic fields at the compass 
and which become relatively more important 





42 


COMPASSES AND ODOGRAPHS 


because of the reduction in strength of the di¬ 
recting field because of the shielding; (3) vi¬ 
brations and shock which produce strictly me¬ 
chanical deviations of the compass and which, 



Figure 36. Trace of map made in medium tank, 
with compass inside armor, showing differences 
between actual and mapped positions at various 
points along route. 

again, are aggravated by the reduced directive 
force because of the shielding. 

A number of test maps and navigational 
problems were conducted with this installation, 
some of which showed quite good results, as, 
for example, Figure 36. 

These tests indicated that with careful atten¬ 
tion to compensation, sufficient accuracy is ob¬ 
tainable to warrant use of the odograph in this 
type of vehicle and that performance with er¬ 
rors of the order of 2 per cent on road mapping 
and 4 per cent on cross-country mapping could 
be obtained if the compass were compensated 
daily. 

Light Tank—Compass Outside 
Armor" 

A series of test installations was made with 
the inductor compass mounted outside the 


armor of a light tank. Separate tests were made 
with the compass mounted 6 in., 10 in., and 25 
in. above the armor. The testing included a 
series of maps made with the M-l land odo¬ 
graph and checks of shifts of compensation 
with the compass in each of the three positions. 
(See Figure 37.) It was found that the shifts in 



Figure 37. M3A1 light tank, showing position 
of compass on outside of armor. 


compensation were quite large with the com¬ 
pass only 6 in. above the armor and that the 
position 10 in. above the armor gave results 
almost as good as those obtained at 25 in. 



Figure 38. Map made in light tank with induc¬ 
tor compass mounted 10 in. above tank armor. 


above the armor. In the 10-in. and 25-in. posi- 


































REPORTS ON TEST INSTALLATIONS 


43 


tions, fairly satisfactory maps were obtained 
(Figure 38), although the compensation shifts 
with time and mileage amounted to 2 degrees to 
4 degrees for a long run, with these shifts dis¬ 
appearing to a certain extent after the tank 
stands overnight. In the 10-in. and 25-in. posi- 


Motor Sled and Other Snow 

Vehicles 4 ’ ° 

These tests were carried out to determine the 
applicability of the odograph to snow tractors 
and motor sleds. Two types of installations 




SCALE IN MILES 
2 4 


6 


Figure 39. Figure 40. 

Map made in half-track personnel carrier. 


tions, the compass compensation was not ma¬ 
terially affected by opening the doors on the 
front of the tank or on the gun turret, or by 
rotating the gun turret by 90 degrees from its 
normal position. 

These tests indicated that quite satisfactory 
odograph performance may be obtained in 
tanks with the compass mounted outside the 
armor. 


166 Half-Track 3 

This installation used a DTM compass and 
Monroe integrator. Some of the maps result¬ 
ing from this test were rather poor because of 
incomplete compensation and difficulties result¬ 
ing from change of the magnetic state of the 
vehicle. However, several maps with good clo¬ 
sure were obtained, as are illustrated by Fig¬ 
ures 39 and 40. 

The general conclusions of this test were that 
the half-track personnel carrier is a suitable 
vehicle in which to mount the odograph, and 
that the magnetic compass should hold compen¬ 
sation for a period of from three to six days or 
from 100 to 400 miles of mapping. 


were made, i.e., (1) on the tractor itself, and 
(2) on a cargo-carrying sled. The installations 
used the standard Monroe compass and the 
Monroe integrator, either driven by a speed¬ 
ometer cable (when installed on the vehicle 
itself) or by a Monroe log pickup unit (as used 



Figure 41. T-26 snow tractor with trailer (on 
wheels) equipped with odograph. (Note odometer 
wheel behind trailer.) 


in the marine-type installations) when driven 
by impulses from an odometer wheel attached 
to the cargo-carrying sled. The special trailer 
with odometer wheel is shown by Figure 41. In 
this installation, the integrator was mounted in 
the operator’s seat of the T-26 snow tractor 
with electrical connection to the odometer wheel 







44 


COMPASSES AND ODOGRAPHS 


through a log pickup unit which feeds one rota¬ 
tion of the drive shaft into the odograph by 
means of a clutch onto the electric motor each 
time an impulse is received from a contact 


able in accuracy with those obtained on other 
vehicular installations. Maps made by installa¬ 
tions in snow vehicles are shown as Figures 44 
and 45. 



Lake, Colorado. 

Figure 43. General arrangement of equipment 
on M-29 cargo carrier. 



DIRT ROAD COVERED WITH 2 FEET OF SHOW 
COHS/STIHC OF 6 TO 8 IHCHES OF LIGHT 
SHOW OH /« TO 18 IHCHES OF HARD CRUST 


SCALE OF MILE 

0.0 O.S 1.0 

I-1-1-1- > 


Figure 44. Maps made with odograph in special trailer, Mt. Rainier National Park. 


mechanism operated by the odometer wheel. 1 - 6 - 8 2 1 /?-Ton Amphibious Truck 

The general arrangement on the M-29 cargo- (DUKW) 6 

carrying tractor is shown by Figures 42 and 43. 

The general results of these tests were quite 
satisfactory and the maps made were compar- 


The amphibious installation requires an indi¬ 
cation of distance traveled from operation 



















REPORTS ON TEST INSTALLATIONS 


45 


\ 



APPROXIMATE LOCATION OF TRAILS 
GIVEN BY MAP 

ODOGRAPH RECORD OF TRAILS 


Figure 45. Trail reconnaissance with odograph in M-29 tractor, Camp Echo Lake, Colorado. Dashed 
lines: trails on map; solid line: route as mapped by odograph. 


either on land or in the water. This was done by 
providing a log pickup unit (Stavrokov) for 
providing distance traveled in the water and a 
speedometer cable (operating electric contacts 
instead of directly into the integrator) for pro¬ 
viding distance traveled on land. Electric im¬ 
pulses from either the water log or speedometer 
cable operate a standard model log pickup unit, 
as built for the marine application of the odo¬ 
graph, and it is only necessary to operate an 
electric switch to shift from the speedometer 
pickup for land operations to the log pickup for 
water operation. The installation used a stand¬ 
ard Monroe compass and the IBM vehicular 
(ratchet drive) odograph, and was mounted as 
shown by Figure 46. 

No provision is made in these installations 
for any correction for drift of the boat with the 



Figure 46. Odograph installation on amphibious 
truck (DUKW). Impeller in board (just forward 
of partition) for travel on land. Left, compass; 
center, plotting unit; right, log pickup unit. 














46 


COMPASSES AND ODOGRAPHS 



Figure 47. Odograph record made in DUKW, partly on land, partly in water. Large error is due to 
drift caused by current in water. 


water. Therefore, the maps made (as shown by 
Figure 47) show large errors of closure on ac¬ 
count of currents in the water. 

These tests indicated that, on account of the 
slow speed in the water and the consequent 
relatively large disturbances caused by tidal 
and other currents, an odograph is not likely to 
prove particularly useful in amphibious vehicles 
of this type. 

169 B-18 Army Bomber™’ le 

This test installation used a Pioneer fluxgate 
compass, a Schwien true airspeed meter, and 
an early model of the IBM disk drive integrator. 
Test flights were made in September and 
October 1942. 

The integrator had no provision for compen¬ 
sation for air drift but such drift could be de¬ 
termined and the maps corrected accordingly 
by successive flights over the same point (Fig¬ 
ure 48), or by calculating corrections from wind 
direction and velocity, as estimated from drift 
sights (Figure 49). 

These were the first tests of the airborne odo- 



i-1-1 

Figure 48. Odograph map in B-18 Army 
bomber; Ci, Co, C 3 , C 4 are successive mappings of 
the same point. Wind vector can be derived from 
time interval and distances between successive 
mapped positions. 











REPORTS ON TEST INSTALLATIONS 


47 


graph and were important in showing the gen¬ 
eral practicability of the device and the desira¬ 
bility of including a device for setting wind 


stallation used the Pioneer fluxgate compass, 
the Schwien true airspeed meter, and the IBM 
disk drive integrator with provision for wind 



I_1- I 

Figure 49. Odogaph map in B-18 army bomber, showing positions as mapped, as calculated by allowing 
for wind drift determined by drift sights, and actual positions. 



Figure 50. Odograph map in B-24 Army bomber, 
showing search flight with successive returns to 
the same point. Total flight 100.5 miles; closure 
error 1,150 yd, or 0.7 per cent. 

drift automatically (which was later incorpo¬ 
rated into the integrator). 

16 10 B-24 Army Bomber 1 ’ 1 

Test flights of an installation on a B-24 
bomber were made in February 1943. The in¬ 



Figure 51. Odograph map in B-24 Army bomber. 
Successive returns to a wrecked ship. Total flight 
104.9 miles; closure error 2,280 yd or 1.2 per cent. 


correction. The entire installation as used in 
this test (using the earlier, Type AO-2 inte¬ 
grator) weighs approximately 150 lb. 

The tests indicated good performance pro¬ 
vided that the wind is accurately determined 
and the pilot flies ball-banked turns and main¬ 
tains constant altitude. Under these conditions, 









48 


COMPASSES AND ODOGRAPHS 


banks up to 60 degrees could be made, and the 
odograph would still function properly. After 
determining wind (in the manner indicated by 
Figure 44) and setting the wind correction into 
the integrator, some very good flights were 
made, as are indicated by Figures 50 and 51. 


mileage unit, a quite successful map was made, 
as is shown by Figure 52. 

These tests were of very limited scope and 
added little to previously available information 
concerning performance and utility of the in¬ 
strument. 


N 



Figure 52. Odograph map in RA-29 for flight from Wright Field to Columbus and return. Wind 
correction from meteorological observations. 


These were the first tests made with the in¬ 
clusion of automatic wind drift correction and 
showed that very good maps could be made of 
the position of a plane with respect to the 
ground. It is probable (although not so recorded 
in the reports) that these tests were important 
in indicating performance good enough to stim¬ 
ulate the interest of the Services in this device. 


1-611 Army Patrol Plane, Type RA-29 ' 

This installation used the Pioneer fluxgate 
compass, Pioneer air mileage unit, and IBM 
disk drive integrator. After considerable trou¬ 
ble on account of the inaccuracy of the air 


1612 Model OA10 Aircraft 

(Flying Boat) 7 

This installation used a Pioneer fluxgate com¬ 
pass, a British air mileage unit, and IBM disk 
drive integrator with wind correction and re¬ 
mote electrically operated plotting table. Spe¬ 
cial items of installation included a pitot tube 
head, mounted above the bombardier’s compart¬ 
ment, and watertight valves that had to be in¬ 
stalled in the flushing lines of the air mileage 
unit so that these lines could be closed during 
landing or take-off on the water. The general 
nature of the installation is shown by Figure 
53, with the auxiliary equipment shown by Fig¬ 
ure 54. A number of difficulties with the acces- 


tfctfflMMKJ ■' i 









49 


REPORTS ON TEST INSTALLATIONS 


sories, particularly with the air mileage unit 
and compass unit, were experienced with this 
installation, but these were finally eliminated 
and quite successful maps produced, as indi¬ 
cated by Figure 55. 

These tests indicated at that time (November 
1943) that the aerial odograph was a useful 
navigational instrument, capable of a high de- 


made to determine: (1) the accuracy with 
which winds could be found with the odograph 
itself; (2) the possibility of using other than 
visual fixes for wind determination; (3) the 
usefulness of the odograph in dead-reckoning 
navigation; (4) the value of the instrument in 
supplying a record of a flight and, in particular, 
one in which a search is made; (5) the applica- 



Figure 53. Odograph installation on Army Patrol Flying Boat (OAIO 43), showing integrator, plotting 
table, caging switch for compass gyro, and master indicator mounted in navigator’s compartment. 


gree of accuracy when used with reasonable 
skill and care. 

1 613 PBM-3S (Navy Patrol Flying 
Boat) 8 

This installation (December 1943) used a 
Pioneer fluxgate compass, a British air mileage 
unit, and IBM disk drive integrator with wind 
correction. The general arrangement of the in¬ 
stallation is shown by Figure 56. The tests were 


bility of the odograph to magnetic airborne 
detector [MAD] work. 

In general, the results of this test were quite 
satisfactory, and an indication of the general 
nature of the mapping obtainable is shown by 
Figure 57. The manner in which the odograph 
may be applied to a search pattern is indicated 
by Figure 58, and the manner in which a MAD 
search might be conducted is simulated by fol¬ 
lowing the course of a ship, as is indicated by 
Figure 59. 











50 


COMPASSES AND ODOGRAPHS 



Figure 54. Auxiliary equipment for installation of Figure 53, mounted beneath navigator’s table. 


The tests indicated that wind determinations 
by means of the odograph could be made quite 
accurately, that radar and radio cone of silence 
may be used to find winds with an accuracy 
comparable to that obtained when using visual 
fixes, that in dead reckoning the odograph 
would be particularly valuable in case of eva¬ 
sive action, and that the instrument should be 
particularly valuable for search flights and 
MAD work. 

17 MISCELLANEOUS DEVELOPMENTS 
AND TESTS 

Lateral Activities within the 
Compass and Odograph Project 

During the nearly five years in which it was 
active, many relatively minor development 



Figure 55. Odograph map made in test flight 
from Boston to New York. 


projects were included within the general ac¬ 
tivities of the compass and odograph project. 




















MISCELLANEOUS DEVELOPMENTS AND TESTS 


51 



Figure 56. Odograph installation on Navy Flying Boat (PBM-3S). 









52 


COMPASSES AND ODOGRAPHS 


These were undertaken either because they 
were closely related to the principal develop¬ 
ments or because the personnel of the project 


Those that are included are more or less definite 
and completed projects which are mentioned in 
the various current reports. 



Figure 57. Odograph map made in navigational flight from Point Judith to Cape May for comparison 
with navigator’s dead-reckoning and return flight from Cape May to determine odograph error. 


were particularly well suited by training, ex¬ 
perience, and equipment to undertake them. 
Many of these smaller jobs were taken up as a 
result of direct requests from the military 
Services. 

Of necessity, many of the smaller side-line in¬ 
vestigations and developments, many of which 
because of their failures were useful mainly in 
negative ways, are not included in this report. 


1,7 2 The Pedograph 13 

The pedograph is essentially a small odo¬ 
graph designed to be carried by a man on foot 
and to make a map of the course he travels. 
While such a development was considered in the 
earlier days of the odograph project, it was not 
actually undertaken until requested by the 
Army after interest was aroused by the cap- 


<|0N FIDENTIAL , 















MISCELLANEOUS DEVELOPMENTS AND TESTS 


53 


ture of a Japanese instrument which performed 
this function. 

Principles of Operation 

In the pedograph, a simple magnetic compass 
gives the reference direction. The servomechan¬ 
ism is replaced by the operator himself who 



graph for control. Solid line: odograph trace; 
dashed line: navigator’s dead reckoning. 

turns a cover over the compass to keep a refer¬ 
ence line on the cover parallel with the compass 
needle. The distance is given by a thread which 
is pulled out from a spool in the instrument and 
over a pulley which is thus rotated by an 
amount proportional to the distance traveled. 

The manner in which these two functions are 
integrated to make a map is indicated by Figure 
60. The paper on which the map is drawn is car¬ 
ried on a cylinder or platen which is free to ro¬ 
tate and also to move longitudinally along the 
platen shaft. A plotting wheel in contact with 
the paper is oriented by the rotation of the 
compass follower. This wheel is turned by reduc¬ 
tion gears connected directly to the grooved 
pulley over which the distance-measuring 
thread is paid out so that the rotation of the 
plotting wheel is directly proportional to the 


distance traveled. If the axis of the plotting 
wheel is parallel to the platen shaft, the platen 
will rotate about the shaft. If the axis is per¬ 
pendicular to the platen shaft, the rotation of 
the plotting wheel will cause the platen to move 
longitudinally along the shaft. At intermediate 
positions, the rotation of the plotting wheel 
causes a combination of rotation and longitudi¬ 
nal movement of the platen and thus resolves 
the motion into components parallel and per¬ 
pendicular to the platen shaft, thereby perform¬ 
ing the required functions of the odograph inte¬ 
grator. A fixed pencil will then make a trace on 
the map paper which will record the motions of 



successive observations on a moving ship, from 
which its speed and course were determined. 

the cylinder under the pencil and thereby trace 
a map of the course over which the instrument 
is carried. 

The Completed Instrument, 

Accessories, and Tests 

The general construction of the instrument 
as actually built, and using the principles indi- 











54 


COMPASSES AND ODOGRAPHS 


cated by Figure 60, is shown by Figure 61. In 
addition to the fundamental requirements, the 
completed instrument contains, as accessories, 
an automatic threader which facilitates passing 


by the simple expedient of providing two driv¬ 
ing pulleys of different diameters. 

The instrument uses standard cotton threads 
and sizes from No. 40 to No. 60 produce good 


CO 4PASS-CARO REFERENCE¬ 
LINE 


COMPASS-HOUSING REEERENCE- 
UNE 



PAPER-RETAINER 
CLIP 


Figure 60. Schematic diagram of pedograph, showing general principles of operation. 


the thread through the guides- and around the 
grooved pulley, a marking device which permits 
reference marks to be placed on the map by a 
knob on the outside of the instrument, and small 
flashlight lamps for illuminating part of the 
map surface. Two different scales are provided 


results. Number 40 thread with a tensile 
strength of about 3 lb was adopted as standard. 
(A spool holding 2,000 yd of camouflage thread 
was specified.) Map paper size is about 6 x 11 in. 
Total weight of the instrument is 6 V 2 lb. 

A number of tests of the instrument were 


B 


























































MISCELLANEOUS DEVELOPMENTS AND TESTS 


made in a rough wooded area. These indicated 
an average accuracy based on errors of closure 
of somewhat better than 3 per cent. Procure- 



Figure 61 . Oblique front view of pedograph 
with cover open and platen at extreme right end 
of platen shaft. (1) Plotting wheel, (2) spool of 
thread, (3) play-off guide, (4) tension device, 

(5) scale eyelets, (6) platen shaft, (7) pencil, 

(8) light, (9) trace sheet retaining clamp, (10) 
platen. 

ment of these instruments was started, and they 
were used in some quantity by troops in the 
Pacific theater shortly before the end of the 
war. 



Figure 62. Schematic diagram of step-writer, 
showing general principles of operation. 


1 " 3 The Step-Writer 1 ' 

The step-writer is another type of odograph 
carried by a man on foot and performs the same 
function as the pedograph. The essential dif¬ 
ference is that the distance is obtained from a 
ratchet operated by a line attached to the leg of 
the operator and that a simple disk is used for 


the map, and this disk is kept oriented so that 
reference lines on it are parallel with a refer¬ 
ence direction given by the compass. 

Principles of Operation 

The general principle of operation is indi¬ 
cated by Figure 62. The ratchet, which is moved 
one or two notches by each step of the operator, 
turns a knurled driving wheel operating on the 
lower side of the disk of map paper. Opposite 
the knurled driving wheel is a knurled inking 
wheel which makes a trace of the course on the 
upper surface of the map paper. A thumb knob 



Figure 63. Top view of step-writer. ( 1 ) Thumb 
screw for orienting map paper, (2) knurled ink¬ 
ing wheel, (3) plunger for distance input, (4) 
map paper, (5) compass needle. 

on the outside of the case operates a roller by 
which the map paper is rotated about the point 
where it is held between the knurled driving 
wheel and the knurled inking wheel. The paper 
is held in the instrument below a compass in a 
transparent case, Figure 63. Thus, if the opera¬ 
tor manipulates the thumb knob so that the ref¬ 
erence lines on the map paper are always paral¬ 
lel with the compass, the motion of the paper 
beneath the knurled inking wheel will always be 
in a direction corresponding to the direction in 
which the operator is traveling. 

Construction, Accessories, and 
Tests of the Instrument 

As made, the simple step-writer does not pro¬ 
vide for producing a map at a standard scale. 







56 


COMPASSES AND ODOGRAPHS 


The scale depends upon the average length of 
stride of the operator. Two scale ratios are pro¬ 
vided by means of a device which limits the mo¬ 
tion of the ratchet so that the wheel is moved by 
either one or two teeth for each step. The gear¬ 
ing is such that the instrument gives map scale 
ratios of 1 to 20,000 or 1 to 40,000 for a 30-in. 
step. The compass was a special development 
and consists essentially of a magnetic needle in 
a bowl of transparent plastic filled with kero¬ 
sene for damping. The total weight of the in¬ 
strument is 4 lb. The circular map paper has a 
diameter of 3 Yl in. (which corresponds to a dis¬ 
tance of about 1 mile, at scale 1:20,000 and 
about 2 miles at 1:40,000). 

Field trials indicated that over moderately 
smooth territory a closure error of the order of 
1 per cent would be expected. The effects of 
going uphill or downhill were checked and, 
rather surprisingly, it was found that there was 
little difference in the length of a step and 
therefore in the precision of the instrument. 
Tests with the operator walking through under¬ 
brush showed that after some experience the 
average step in the brush was only some 2 to 5 
per cent shorter than on a road. 

In general, the step-writer is considerably less 
precise than the pedograph and has the further 
disadvantage of a much smaller mapping area 
( 31 / 2 -in. circle vs a 6xll-in. rectangle). It has 
the advantage of lighter weight (4 lb vs 6(4) 
and, from a military standpoint, the very im¬ 
portant advantage of having no telltale thread. 


Miscellaneous Supplementary 
Developments 

Landing Craft Compasses 16 

A special compass for landing craft was de¬ 
veloped to have a period of oscillation that 
would not respond to the usual period of roll of 
landing craft. A production model similar to the 
prototype developed under the compass project 
was manufactured by the Navy in large quanti¬ 
ties for use on landing craft, PT boats, and 
other vessels. 

Redesign of No. 1 Compasses 16 
Under the compass project, DTM partici¬ 


pated in the redesign of the Navy No. 1 (714- 
in.) compass. Modifications of the magnet and 
damping system and compensating system 
greatly reduced the spurious deviations from 
various sources. The modifications were 
adopted in the manufacture of all compasses 
of this general type. 

Redesign of Magnesyn Compass 16 

It was found that the magnesyn compass 
such as is used for a repeater indicator on ships 
was subject to serious oscillations from rolling 
of the vessel. A swinging mast some 45 ft high 
was constructed and used to test compasses, 
and, from these tests, the standard compass 
was modified to give greatly improved perform¬ 
ance on ships. 

Design of New 6-in. Compass 16 

Design work and model construction were un¬ 
dertaken for a new compass with compensation 
based on experience gained in the general com¬ 
pass development. Its eventual use on many 
ships in the Navy is anticipated. 

Odograph Attack Plotter 16 

In cooperation with the Underwater Sound 
Laboratory, the marine odograph was adapted 
to plot the attack of a ship on a submarine. This 
involved the construction of a separate stylus 
so that the position of both the attacking vessel 
and the submarine were shown continuously on 
the map. 

Power Supply Sources and 
Converters 

All the odograph installations require a spe¬ 
cial power source of some sort to supply electric 
currents at the voltages and frequencies re¬ 
quired for the electronic tubes and other de¬ 
vices. Therefore, it is necessary to provide an 
accessory unit to convert the electric supply 
from the primary source (usually storage bat¬ 
teries) to that which is applicable to the ap¬ 
paratus. 

For the vehicular odograph installations, a 
commercial power supply unit (manufactured 
by General Electric Company) was used with 
some modifications. This operates on the same 


IAL 




MISCELLANEOUS DEVELOPMENTS AND TESTS 


57 


general principle as the power supply units 
used for automobile radios wherein a low-volt¬ 
age, direct-current supply from storage bat¬ 
teries is converted, by the use of a vibrator and 
appropriate amplifier and filter circuits, into 
the high voltage required for the thyratrons and 
other electronic tubes and apparatus used in the 
equipment. 

For the airborne installations, the fluxgate 
compass requires an electric supply at a fre¬ 
quency of 400 c. The same supply is required 
for certain repeater compass installations on 
ships which use the autosyn motor principle to 
repeat the compass indication at various points. 


Ordinarily, this 400-c supply is provided by 
means of a rotary converter which is part of the 
aircraft equipment and which was not part of 
the odograph or compass development. 

One special development 11 in power supply 
units which was undertaken under the compass 
project was that of providing an electronic in¬ 
verter to take the place of the rotary converter 
to furnish the 400-c supply for repeater com¬ 
passes on ships. The electronic inverter devel¬ 
oped under this project is somewhat more flex¬ 
ible as to primary power supply than the rotary 
converter and furnishes an output with some¬ 
what better electrical characteristics. 




Chapter 2 

T-58 PHOTOFLASH FUZE 

By George E. Beggs, Jr. a 


21 INTRODUCTION 

T he purpose of this project 6 was to develop a 
means of synchronizing the firing of a fall¬ 
ing photoflash bomb with the operation of an 
aerial camera located in the aircraft from which 
the bomb was released. Further, it was re¬ 
quired that the equipment be designed for auto¬ 
matic sequential release and firing of a number 
of bombs, i.e., firing in train. In other words, 
bombs were to be released automatically at con¬ 
stant intervals and fired in turn automatically 
after a given time delay. At the same time, the 
camera shutter was to be operated automati¬ 
cally at the correct instant to synchronize with 
the firing of each bomb. The release and firing 
delay intervals were to be adjustable inde¬ 
pendently in increments of 1 second from 5 to 
90 seconds. Synchronization was to be accom¬ 
plished to an accuracy of a few milliseconds. 
Such operation would make possible exposures 
at any desired rate and at any altitude within 
the ranges normally required. 

Early attempts at night photography involved 
the obvious exposure method of opening the cam¬ 
era shutter and allowing the duration of the bomb 
flash to determine the exposure, after which the 
shutter would be closed. Such procedure pro¬ 
duced blurred images because of the motion of 
the plane, making high-definition photography 
impossible at high altitudes. The problem be¬ 
came more and more serious as higher-speed 
planes were used for photographic work and as 
more and more night photography became nec¬ 
essary because of changes in theaters of opera¬ 
tion. A later solution of the problem of syn¬ 
chronization was attempted by the introduction 
of a photocell to control the camera shutter, the 
photocell being actuated by the initial light 
from the bomb. This method proved reasonably 
satisfactory from the standpoint of synchroni- 


a Technical Aide, Section 17.1-17.2, NDRC. 
b OD-141. 


zation, but it did not allow the firing of more 
than one bomb at a time for increased illumi¬ 
nation in a given picture. Also it did not cir¬ 
cumvent the problems of jamming caused by 
searchlights, antiaircraft bursts, and other 
extraneous light sources. 

It was obvious that to take full advantage of 
the possibilities of night photography, the 
camera shutter should be opened only for a 
brief exposure during the peak light intensity 
of the photoflash bomb, and the system should 
be relatively free from jamming and should 
allow the control of one or more bombs in salvo 
or in train. 

Numerous methods of accomplishing the de¬ 
sired results, more fully outlined in Section 2.2, 
were considered and several attempted. The 
final apparatus, which performed successfully 
in initial field tests, consists of the T-58 fuze 
with an associated time delay arming device 
known as the T-4, the synchronizer, the radio 
transmitter, the intervalometer, and associated 
controls within the aircraft. This apparatus op¬ 
erates on the principle that basic control is es¬ 
tablished by the transmission of a coded radio 
pulse from the aircraft to the bomb. This radio 
pulse initiates the action of the bomb by means 
of a radio receiver and control circuit contained 
in the T-58 fuze. This same pulse activates the 
camera shutter with appropriate time delay to 
account for mechanical delays within the rest 
of the system and for delays within the bomb 
ignition train itself. 


2 2 MILITARY REQUIREMENTS 

The original military requirements were sub¬ 
mitted as Service Project OD-141 on October 4, 
1943, by the Office of the Chief of Ordnance. 
They were originally established by the Army 
Air Forces, as the branch of the Armed Serv¬ 
ices initiating the request for the new type of 


58 



SUMMARY OF DEVELOPMENT 


59 


ordnance equipment. The requirements set 
forth in the original correspondence are listed 
below: 

1. Synchronization shall be effected by an 
improved method, initiated from either mem¬ 
ber of the bomb-camera combination to the 
other member. 

2. There shall be provision for adjustment 
(after take-off of the airplane) of the time de¬ 
lay between release and burst of the bomb over 
a range between 15 and 90 seconds. 

3. There shall be provision for optional open¬ 
ing or closing of a magnetic circuit in the 
camera to initiate action of the shutter at an 
instant selectively variable between 0.003 sec¬ 
ond before and 0.005 second after the initial 
emission of light from the photoflash bomb. 

4. There shall be a time delay safety provi¬ 
sion equivalent to the spinner action on the 
Mill fuze, to prevent premature arming and 
firing of the bomb. 

5. The apparatus shall operate for any space 
between bomb fuze and camera up to 45,000 ft. 
All component parts must perform satisfac¬ 
torily between the temperature limits of —40 
F and +70 F. 

6. The equipment shall be of such nature that 
it can be successfully stored for prolonged pe¬ 
riods at temperatures between —65 F and 
+160 F. 

7. There shall be protection against any pos¬ 
sible interference from enemy or from other 
sources. 

8. Provision shall be made for preventing 
premature operation of the photoflash bombs 
during descent on occasions when several 
bombs may have been released in train. Under 
such conditions, no bomb is to function until it 
has accomplished the required descent. 

9. The firing mechanism is to function upon 
impact if the bomb falls to the ground in armed 
condition. Since the characteristics of photo¬ 
flash powder are such that safe dropping of the 
bomb with such loading cannot be guaranteed 
when released from a height of 8,000 to 10,000 
ft onto normal soil, the fuze is not required to 
withstand impact when dropped “safe” from 
these heights. The fuze shall, however, be capa¬ 
ble of being dropped 25 ft onto a hard surface 
without functioning. 


23 SUMMARY OF DEVELOPMENT 

Consideration of the military requirements 
made it apparent that there were several meth¬ 
ods of attack which might satisfactorily meet 
the majority of them. It was quite apparent that 
radio control of the system was most desirable, 
in view of previous work in the field of photo¬ 
flash synchronization and available data on 
small electronic components for use in airborne 
vehicles such as a bomb. One of the major prob¬ 
lems presented was the determination of 
whether the control should be from bomb to 
camera or from camera to bomb. Practical con¬ 
sideration of these two methods led to the 
choice of the latter, for a number of reasons. 
There was, for instance, the problem of simul¬ 
taneous firing of several bombs in salvo. Also, 
high-altitude night photography required that 
the distance between the camera and the photo¬ 
flash bomb be of the order of several miles (45,- 
000 ft). Sufficient radio-frequency power to 
bridge this gap requires transmitting equip¬ 
ment too bulky and heavy to be accommodated 
in the bomb without increasing its physical size 
and shape materially. Thus it was decided to 
place the heavy transmitting and control equip¬ 
ment in the aircraft and to equip the bomb with 
a small, simple, and relatively insensitive radio- 
operated receiver-type fuze, designated as T-58. 
The automatically keyed transmitter emits an 
r-f pulse of approximately 2 milliseconds’ dura¬ 
tion, appropriately coded by various means to 
prevent easy jamming of the radio signal. 

The major development was divided into a 
number of individual ones corresponding to the 
following units of equipment: (1) multiphase 
intervalometer, (2) synchronizer, (3) radio 
transmitter, and (4) bomb fuze receiver. 
These units perform widely different func¬ 
tions, some mechanical and others electric. 

The multiphase intervalometer is an appara¬ 
tus which determines the rate at which the 
bombs are released, the delay in firing after re¬ 
lease, and the rate at which photographic ex¬ 
posures are made. In normal operation, it would 
be preset before take-off according to the re¬ 
quirements of the photographic mission. It is 
adjustable in increments of 1 second from 2 to 
120 seconds. 



60 


T-58 PHOTOFLASH FUZE 


The synchronizer is a unit which provides 
electronically a time delay between the firing 
of the photoflash bomb and the operation of the 
camera shutter. The purpose of the delay is to 
cause the exposure to occur during the optimum 
period of light. The delay is necessitated by the 
fact that mechanical inertia within the shutter 


and delay within the bomb ignition train make 
it impossible to transmit simultaneously pulses 
for control of both items. The synchronizer is 
adjustable in increments of 2 milliseconds from 
5 to 25 milliseconds, thus allowing adjustment 
for different types of photoflash bombs and 
cameras. 



Figure 1. Photograph taken during Test 5 (photograph by Ballistics Research Laboratory, Aberdeen 
Proving Ground). 




SUMMARY OF DEVELOPMENT 


61 


The radio transmitter emits a 2-millisecond 
pulse signal whenever keyed by the synchro¬ 
nizer. At all other times, there is no emission 
from the radio transmitter. Transmission is at 
a radio frequency of 120 to 130 me. 



Figure 2. Airborne multiphase intervalometer. 


The bomb receiver is built into a radio-oper¬ 
ated fuze which replaces the standard Mlll-A 
fuze. The pulse received from the radio trans¬ 
mitter is rectified by means of a grid-leak detec¬ 
tor, amplified, and applied to the grid of a thy- 
ratron tube to initiate the firing train. 

These various items, when combined into a 
complete operating system, meet the majority 
of the military requirements. Field tests, as out¬ 
lined below, were completed as part of the proj¬ 
ect. Eight tests are outlined. Six were conducted 
at Aberdeen Proving Ground, Maryland, with 
the assistance of the Ordnance Department; the 
other two, at Denver, Colorado, with the assist¬ 
ance of the Army Air Forces. 

Test 1. Safe-Drop Test from Tower, Using 
Inert Loaded Bombs. In this test, ten bombs 
with completely operable fuzes were dropped 
from a tower at a height of 50 ft, to see if the 
impact would cause fuze operation. No fuzes 
operated. 

Test 2. Arming Characteristics. With a set¬ 
ting of 90 degrees for the rotor containing the 
firing squib, a test was conducted to measure 
the time from release of the bomb from the air¬ 
craft to earliest possible fuze function. The con¬ 
trolling transmitter was pulsed approximately 
four times a second to allow determination of 
fuze function within 0.25 second after time of 


arming. Arming-time delay was provided only 
by internal characteristics of the bomb involv¬ 
ing the gear train powered by the wind-driven 
propeller on the generator and rotating the 
rotor through 90 degrees to the point of firing. 
M46 bombs were supplied with spotting charges 
for this test. It was found that under no con¬ 
ditions did the bomb explode too close to the 
aircraft from the standpoint of safety and that 
results were more than adequate from the stand¬ 
point of consistency. 

Test 3. Accuracy of Synchronization. A 
ground test was conducted to determine the 
synchronization accuracy between the fuze fir¬ 
ing, the bomb firing, and the camera shutter 
opening. A dummy bomb was utilized as a re¬ 
ceiving bomb connected to an active bomb by 
twisted-pair wire to avoid destruction of a 
large number of test fuzes. The data were 
taken on a multichannel cathode-ray recording 



Figure 3. Side view of airborne multiphase in¬ 
tervalometer. 

oscillograph. Synchronization of the order of 2 
milliseconds, or better, was obtained in the 
numerous firings completed. Data on the accu¬ 
racy and consistency of camera and bomb op¬ 
eration were also obtained. 

Test U. Radio-Link Range. A test was made 
to check the radio-link range using a B-17 air¬ 
craft with equipment installed and a standard 
fuze mounted well above the ground on an M46 
bomb. Adequate operation over a range of 45,- 
000 ft was obtained with the bomb and aircraft 
maintained in relative positions similar to those 
expected in actual practice. 

Test 5. Check on Operation, Involving Single 
Bombs. This test consisted of a check on the 
operation of the apparatus by dropping single 
bombs (not several in train) and firing by radio 








62 


T-58 PHOTOFLASH FUZE 


link. This test included taking of photographs. 
(See Figure 1.) Good synchronization was ob¬ 
tained, as checked by a recording cathode-ray 
oscillograph and a photocell at a ground loca¬ 
tion. The oscillograph compared the photocell 
pulse picked up from the bomb with a pulse 
from a contact made during the camera shutter 
operation. 

Test 6. Check on Operation, Involving Three 
Bombs in Salvo. The final test at Aberdeen in¬ 
volving the dropping of three bombs in salvo 
was successfully completed with all bombs fir- 
VARIABLE FROM 2-120 SEC 


BOMB-RELEASE PULSE 


24 DESCRIPTION AND TECHNICAL 

INFORMATION 

241 Multiphase Intervalometer 

The multiphase intervalometer, illustrated in 
Figures 2 and 3, is made up of three mechanical 
timing devices driven by a single 28-volt d-c 
motor. Essentially, the device must perform the 
following functions. After a starting signal is 
received, it must operate periodically at some 
predetermined time interval. It must perform 


L 


FIRING PULSE 


2.5 MSEC-H 


2-120 SEC- 


3-2 5 MSEC- 


CAMERA-ACTUATING PULSE 


L 


Figure 4. Pulse sequence for intervalometer and synchronizer. 


ing simultaneously and with good syiichroniza- 
tion. Pictures taken indicated far more light 
than expected, producing overexposure of the 
initial pictures taken under the same conditions. 

It might be mentioned that during the first 
six tests of the last 39 fuzes, 34 performed per¬ 
fectly. The failures in the first few fuzes were 
due to oscillation of the bomb, apparently 
caused by incorrect trail plates. These plates 
were later corrected, so that 100 per cent opera¬ 
tion was obtained in the last 30 drops. 

Tests 7 and 8. Overall Flight Tests. These 
tests consisted of a final check on the apparatus 
wherein bombs, dropped and fired in train, were 
used to take pictures to see if the complete sys¬ 
tem sufficed for actual night photography of a 
reasonable area of ground. These tests were 
completed fairly satisfactorily at Denver. 


a second operation sometime later without any 
interference between the two operations. 
Finally, it must repeat the complete cycle for a 
considerable time. Such a sequence of events is 
required since on a typical mission it might be 
necessary to release bombs and make exposures 
at intervals of 10 seconds, with the exposures 
coming 35 seconds after each bomb is released. 
Under these conditions, since the first bomb 
was released at “zero” time, four bombs would 
be in the air before the first one was fired. After 
the first firing, succeeding bombs would be fired 
at 10-second intervals. Control of release and 
firing pulses for this type of operation can be 
obtained with the multiphase intervalometer 
noted. Construction is such that two Fairchild 
B-3-B intervalometer units are geared to one 
motor drive and modified to perform the re- 



































DESCRIPTION AND TECHNICAL INFORMATION 


63 


quired functions. This eliminates any possibil¬ 
ity of lack of synchronization between two or 
more separate intervalometers driven by sepa¬ 
rate motors. The overall time accuracy is thus 
reduced to the time accuracy of one machine, 
and the lack of synchronism between the drop¬ 
ping and firing pulse is removed. 

The output of this intervalometer provides 


curately timed pulses: one which actuates the 
camera shutter, and another which keys the 
transmitter. Thus the intervalometer and the 
synchronizer provide three pulses: one which 
drops the bomb, one which actuates the radio 
transmitter, and one which actuates the camera 
shutter. The time delay between the last two 
pulses may be varied from 5 to 25 milliseconds 





Figure 5. Block diagram of overall system in aircraft and in bomb. 


two electrically isolated, mechanically timed 
pulses. The first actuates the bomb release 
mechanism; the second, the synchronizer unit. 


Synchronizer 

The synchronizer, or electronic time delay 
mechanism, receives an actuating pulse from 
the intervalometer and divides it into two ac- 


in increments of approximately 2 milliseconds. 
Figure 4 shows the relative timing sequence: 
the bomb release pulse from the intervalometer, 
and the two synchronizing pulses from the syn¬ 
chronizer. Figure 5 is a block diagram for the 
overall system contained within the aircraft 
and within the bomb. 

It was known that the bomb requires approxi¬ 
mately 25 milliseconds to ignite and to reach 
the optimum light period and that the camera 















































































































64 


T-58 PHOTOFLASH FUZE 


shutter requires 10 to 12 milliseconds to open 
completely after receiving the actuating pulse. 
From these two figures, it is clear that, to ob¬ 
tain the desired synchronization, the camera 


transmitter of this type, it was possible to use 
a single 829-B tube in the output and a rela¬ 
tively small low-current-type rectifier power 
supply. The transmitter pulse is modulated with 



pulse should be delayed some 12 to 15 millisec¬ 
onds with respect to the firing pulse. This was 
confirmed in the Aberdeen tests mentioned in 
Section 2.3. 


Radio Transmitter 

The radio transmitter is a pulse-emitting 
type capable of delivering approximately 7- 
kilowatt peak r-f power at a carrier frequency 
between 120 and 130 me. The transmitter has 
no emission whatever, except when keyed “on.” 
In view of the extremely low-duty cycle of a 


23 kc. The power supply equipment for the 
transmitter is such that it can produce full- 
power output pulses as rapidly as once every 5 
seconds, which is the maximum rate of exposure 
of most standard automatic aircraft cameras, 
while more rapid pulsing may be obtained if 
less power output is acceptable. A schematic 
diagram of the pulse transmitter is shown in 
Figure 6. 


Bomb Receiver 

The bomb receiver is comprised of a complete 
























































































DESCRIPTION AND TECHNICAL INFORMATION 


65 


radio receiver, a tuned circuit to respond to the 
23-kc modulation, a wind-driven generator to 
supply plate and filament power, and a power 
supply filter and rectifier for the B supply. An 
internal gear train drives a rotor containing the 


General Characteristics 

Figure 12 shows the T-58 fuze mounted on a 
standard M46 bomb. The component parts of 
the fuze itself are shown in Figure 9. The vari- 



electrically detonated squib for arming delay 
within the fuze. For firing the squib, a thyra- 
tron is used which derives its power from the 
filter condenser in the main power supply. The 
schematic circuit is shown in Figure 7. Opera¬ 
tion of the unit is initiated after release of the 
bomb from the aircraft by the jettisoning of a 
mechanical arming device (T-4) mounted on 
the ring at the end of the fuze unit. (See Figure 
8.) This arming device, developed under an¬ 
other contract, prevents multiple firing of a 
train of bombs in any order other than that in 
which they are dropped. This is done by estab¬ 
lishing a time relation between the arming de¬ 
vices and the intervalometer in the aircraft so 
that there are no periods of time during which 
two receivers are activated and in condition to 
fire a bomb upon reception of a pulse. 


ous pieces of airborne apparatus are shown in 
Figure 10, which is the synchronizing unit; 



Figure 8. Complete T-58 fuze assembly. 

Figure 11, the radio transmitter; and Figures 
2 and 3, the intervalometer. Of interest as one 































































66 


T-58 PHOTOFLASH FUZE 


VANE UNIT 

HOUSING 

CAP 



UNIT HOUSING 


SAFETY SAFETY BLOCK 

BLOCK RETAINER CAP 




SIGNAL EQUIPMENT 
CAP WITH R F 
ASSEMBLY 



SIGNAL EQUIPMENT 

housing and generator 



ARMING 

GEAR 



ARMING GEAR HOUSING 
WITH SQUIB ROTOR 
HOUSING 


SQUIB 

ROTOR 





RADIO CHASSIS 



Figure 9. T-58 fuze components. 




Figure 10. Airborne synchronizing unit. 


Figure 11. Airborne radio transmitter. 


ON FID ' 











DESCRIPTION AND TECHNICAL INFORMATION 


67 


portion of the development are the items con¬ 
tributing to the difficulty of jamming the re¬ 
ceiver or the radio-link operation. First, the 
radiation reception pattern of the bomb and 
the transmission pattern of the radio transmit¬ 
ter in the aircraft are such that they are mutu¬ 
ally aiding but tend to exclude signals from 
other directions. These patterns were originally 
established by reference to bombing tables, to 
allow determination of bomb attitude and rela¬ 
tion to plane at the desired point of firing. Since 
an LC-tuned amplifier with a Q (a figure of 
merit for a circuit, proportional to the ratio of 
the energy stored to the energy dissipated per 
cycle) of approximately 16 is used in the re¬ 
ceiver, the enemy must satisfy a number of re¬ 
quirements in order to jam the operation of the 
unit. 

1. The appropriate radio-frequency carrier 
must be located. 

2. A pulse on this carrier must be initiated 
at a time when the bomb is in an armed condi¬ 
tion. 

3. The pulse must be of sufficient power to 
actuate the relatively insensitive bomb receiver 
under conditions unfavorable to the reception 
of a signal except from the plane. 

4. The pulse must have 23-kc modulation. 

5. The pulse must be of sufficient duration to 
allow the amplitude to build up in the tuned 
circuit. 

All these features make it extremely improb¬ 
able that jamming would prove effective, espe¬ 
cially since the bomb is in an armed condition 
for only a few seconds prior to firing and since 
only a few bombs may be dropped on any one 
mission. 

To allow adequate test of the apparatus, 135 
T-58 bomb receivers were constructed and used 
in the field tests. During the construction of 
these units, under the supervision of the con¬ 
tractor, engineering details were worked out to 
allow reproduction of these fuzes in quantity. 
Two complete units of airborne apparatus were 
also completed in engineered form to allow their 
reproduction at will. Thus, at the conclusion of 
the project, successful tests had been completed 
on the method of synchronization and the safety 
of the device; engineered designs of apparatus 
were available; production problems had been 



Figure 12. T-58 fuze mounted on M46 photoflash 
bomb. 

worked out in some detail; and operational pro¬ 
cedure had been clarified. 










Chapter 3 

OXIMETERS 


31 INTRODUCTION 

A n oximeter is a photoelectric device which 
. measures the degree of oxygen saturation 
of the blood by measuring the percentage of red 
light transmitted by the subject’s ear. It is 
based on the fact that reduced hemoglobin 
which is dark purple in color absorbs a much 
larger fraction of red light than does oxyhemo¬ 
globin which is bright red. In an ideal optical 
system with only two pigments present, ab¬ 
sorption measurements at two suitably chosen 
wavelengths would completely determine the 
relative proportion of the two pigments. In a 
complex system such as the shell of the ear, 
which contains large and varying amounts of 
light-scattering material and highly concen¬ 
trated packets of pigments, the quantitative re¬ 
lationships are uncertain. It has been found 
possible, nevertheless, by using an instrument 
which compares the transmission of red and 
green light by the ear, to measure the oxygen 
saturation of blood with an accuracy of about 4 
or 5 per cent. This oximeter had been developed 1 
before the beginning of the research under 
NDRC and had been calibrated by the analysis 
of over 100 blood samples taken from arterial 
punctures made at the same time as the oximeter 
readings. A number of such oximeters have been 
made and have been widely used in altitude 
chambers and in hospitals. Unfortunately this 
instrument makes use of a taut-suspension gal¬ 
vanometer which renders it unfit for flight use 
because of the vibration. 

The instruments desired by the Air Forces 
were of two types. First was a device simple 
enough in operation to be used by a flier on 
regular combat missions which would warn 
him when the oxygen content of the blood fell 
below the safe level and which would give the 
warning in sufficient time for him to correct 
the situation. At the time the request was made, 
it was not known whether the oxygen supply 
system being introduced would prove entirely 
satisfactory, and it was thought advisable to 
have an independent check on the flier’s condi¬ 


tion. The instrument developed for this purpose 
was called the oxygen want indicator. Second 
was an instrument which should be as accurate 
and reliable as the oximeters already devel¬ 
oped for laboratory use, but which should be 
so resistant to vibration and change of position 
as to allow it to be used in aircraft. It should 
be a recording instrument and require a mini¬ 
mum of attention. Such an oximeter was needed 
for physiological research studies of high-alti¬ 
tude flying and for the testing of oxygen equip¬ 
ment. This instrument was called the flight 
research oximeter. 


32 OXYGEN WANT INDICATOR 

It was realized early in the work that the 
easiest way to satisfy the requirements of size, 
simplicity, and ruggedness and still have an in¬ 
strument which was capable of detecting gross 
changes in the oxygen content of the blood was 
to sacrifice the two-color principle used in the 
laboratory oximeter and measure the transmis¬ 
sion of the red light only. The photocurrents 
produced by the red light are of the order of 
10 microamperes and can be increased by in¬ 
creasing the area of the photocell, while those 
from the green light are roughly one-thirtieth 
as large. If only the red light is used, the photo¬ 
currents can be measured with a standard air¬ 
craft-type microammeter, and the difficulties of 
size and vibration avoided. Variations in the 
thickness of the ear are taken care of by setting 
the indicator at full saturation while the sub¬ 
ject is breathing pure oxygen. The meter indi¬ 
cates the absolute change in the photocurrent 
rather than the relative change. There is, how¬ 
ever, only a rather narrow range of ear thick¬ 
nesses encountered, and there is a considerable 
gap between a safe oxygen concentration (92 
to 100 per cent) and an imminently dangerous 
one (65 to 75 per cent). As a result, it is pos¬ 
sible to design the indicator so that no one will 
be told he is all right when he should be warned, 
and no one will be warned when he is all right. 58 


CON FI DENT1AL 


68 




OXYGEN WANT INDICATOR 


69 


The ear unit for the oxygen want indicator 
consists of a bank of four lamps outside the ear 
and a barrier layer photocell inside the ear. 



Figure 1 . Sectional view of the ear unit. 


Adjustable stops are provided so that the unit 
can be adjusted to the individual ear with a 
fixed optical path after adjustment. The ear 



Figure 2. Ear cup showing lamps and photocell 
of the oxygen want indicator. 


unit is built into a modified Harvard 5b ear¬ 
phone cup which is sewed into a standard flying 
helmet or mounted on a headband. Figure 1 is 


a cross-sectional diagram of the ear unit. Fig¬ 
ures 2 and 3 are photographs of the ear unit. 

A specially designed iron wire ballast tube is 
used to drop the voltage of the plane’s electric 
system which varies from 22 to 30 volts to the 
6 volts needed for the ear lamp and to keep the 
lamp current constant regardless of variations 
in the supply voltage. Three different types of 



Figure 3. Ear unit mounted on headband. 


indicating unit were developed and are de¬ 
scribed below. 


Model I—Pointer Indicator 

This instrument provided indication on a 
standard meter face with the numbered scale 
replaced by three large divisions, Danger, Low, 
and Normal. It was necessary to use a simple 
photoelectric amplifier to amplify the photocur¬ 
rents about 5 times so as to give full-scale de¬ 
flection on the most sensitive meter movement 
available. A full description of this amplifier 
can be found elsewhere. 513 This instrument 


















70 


OXIMETERS 



Figure 4. Signal light type oxygen want indi¬ 
cator. 

proved satisfactory in flight tests, but it was 
felt that a more striking indication was needed. 
Accordingly, the signal light indicator was de¬ 
veloped. 


3 ' 2 ' 2 Model II—Signal Light Indicator 

This instrument (see Figure 4) was designed 
to give warning of approaching anoxia by 
changing the color of a signal light. Since the 
deflection of the microammeter by the unam¬ 
plified currents was sufficient to do this, the 
photoelectric amplifier was not needed. A small 
lamp mounted inside the meter case and a sys¬ 
tem of a slit and two cylindrical lenses produce 
a concentrated beam of light. The light passes 
through a tricolor flag cemented to the meter 
pointer with the result that the color of the 
light is determined by the current flowing 
through the meter. A variable resistance shunt¬ 
ing the meter is used to adjust the light to blue 
for 100 per cent saturation. A green light then 
indicates a safe oxygen concentration, and a 
red light a dangerous one. The narrow cone 
(30 degrees) of light used for adequate bright¬ 
ness necessitates rather careful alignment of 
the instrument. Another difficulty is that a light 
intensity which will be clearly visible during 


INDICATOR UNIT 













































































FLIGHT RESEARCH OXIMETER 


71 


the day becomes glaring at night. Both of these 
difficulties could probably be corrected, although 
this would require additional adjustments on 
the part of the flier. Fifty of these instruments 
were built by the Central Scientific Company 
and were thoroughly tested both in the labora¬ 
tory and in flight and proved satisfactory. 


3 2 ' 3 Model III—Signal Light 

Indicator with Relay 

Flying personnel who participated in the 
flight tests of the Model II indicator felt that 
the visual signal should be supplemented by an 
additional warning such as an audible signal 
and by a valve which would release a store of 
emergency oxygen. This necessitated the incor¬ 
poration into the indicator of a sensitive relay 
capable of handling the current required to 
operate small power devices. The sensitive relay 
developed to do this has been fully described 
elsewhere. 2 The primary relay is the meter 
movement itself. An auxiliary relay, closed by 
the primary relay, provides an alternate path 
for the current and also periodically separates 
the contacts of the primary relay, thus avoiding 
the welding action which is the principal diffi¬ 
culty with ordinary sensitive relays. The pri¬ 
mary and auxiliary relays in turn control a 
power relay. Five Model III indicators were 
constructed and proved satisfactory in labora¬ 
tory and flight tests. Figure 5 is a circuit dia¬ 
gram of the Model III indicator. 


3 3 FLIGHT RESEARCH OXIMETER 

The flight research oximeter was to be as 
accurate and reliable as the laboratory model, 
but capable of operation in aircraft. The two- 
color principle had to be retained in order to 
achieve the necessary accuracy, but this meant 
that the photocurrents involved were many 
times smaller than those involved in the oxygen 
want indicator. Early attempts 50 at a solution 
involved the development of an antivibration 
mounting for the galvanometer and the use of 
electron-multiplier tubes instead of the barrier 


layer cells. Neither of these proved satisfactory, 
and the final model is the same as the laboratory 
oximeter except that a d-c amplifier is used to 
amplify the weak currents from the photocells 
to the point where they can be recorded on a 
0-5 milliampere meter. The amplifier used is a 
commutator type of d-c amplifier built by Gen¬ 
eral Motors and rebuilt so as to ensure constant 
gain with varying supply voltage. A complete 
description of the amplifier together with cir¬ 
cuit is available elsewhere. 5 ' 1 A 16-millimeter 
motion picture camera is used to photograph 



Figure 6. Flight research oximeter. The Cole¬ 
man ear unit is shown in the foreground. 


the oximeter meter and other appropriate in¬ 
struments such as a watch and altimeter. The 
spring motor of the camera is replaced by an 
electric one which drives the camera at such a 
speed that a picture is taken every 2 seconds. 
Figure 6 is a photograph of the amplifier and 
photorecorder. In addition, there is a box con¬ 
taining the power supply and stabilizing units 
(not shown). The commercially available Cole¬ 
man ear unit is used with the oximeter. It may 
be seen in the foreground of Figure 6. 

The flight research oximeter was tested 
against the standard laboratory oximeter by 
putting ear units on both ears of the same sub¬ 
ject. In altitude chamber tests both at room 
temperature and in the cold, the simultaneous 
readings from the two instruments agreed to 
about 1 or 2 per cent. Flight tests of the instru¬ 
ments showed it to be satisfactory except for 
some short periods of unsteady operation. 




72 


OXIMETERS 


34 EVALUATION AND SUMMARY 

Two different types of oximeter were devel¬ 
oped : a warning device intended for routine use 
in high-altitude flight, and a research instru¬ 
ment of higher accuracy designed for physiolog¬ 
ical research and the testing of new equipment 
under actual flight conditions. Four research 
instruments were constructed and delivered to 
Service laboratories. A satisfactory warning 
indicator was developed and 50 instruments 
were manufactured. The new oxygen supply 
systems introduced at the time of the original 
request proved very satisfactory with the result 
that the need for such a warning device was 
much less than anticipated. Consequently, the 
oxygen want indicator was not adopted for 


regular use. By far the biggest disadvantage of 
the indicator is that it is uncomfortable. The in¬ 
ability of one standard shape of ear unit to fit the 
varying shapes of ears increases man’s natural 
dislike of having any fixed object attached to 
his ear. In addition, the pull of the cables on 
the helmet increases the chance of accidental 
displacement and false indication. Much of the 
difficulty comes from the ear unit’s being 
mounted on the helmet. Should the need for an 
oxygen want indicator as a routine instrument 
ever recur, it should be possible to devise a 
clip-on type of ear unit which would remove 
many of the difficulties. This, with an indicator 
and relay such as used in the Model III instru¬ 
ment, should provide a very satisfactory device 
for warning the flier of approaching anoxia. 


f^fclDENTIAL* 





Chapter 4 

RADIO CHRONOMETER COMPARATOR 


41 INTRODUCTION 

T he aerial mapping of the earth’s surface, 
as carried out by the Army Air Forces, re¬ 
quires the measurement of the location of cer¬ 
tain reference points with a high degree of 
accuracy. This is done by celestial observations 
for which an accurate knowledge of the time 
is essential. The accuracy required is indicated 



Figure 1. Radio chronometer comparator. The 
left-hand side of the cabinet is the radio receiver; 
the comparator dial is in the lower right-hand 
corner. 


by the fact that at the equator one second of 
time is roughly equivalent to 1,500 ft. The radio 
chronometer comparator 1 described in this re¬ 
port was designed to be used with the XA-2 
Zenith camera 2 designed and built for the Army 
Air Forces, although it could be used equally 
well in connection with any of the instruments 
used for celestial observation. 

One of the great advantages of the Zenith 
camera over those devices which involve the 
timing of star passages is that it has an elec¬ 


trically operated shutter which is controlled by 
the chronometer. The errors of personal judg¬ 
ment involved in timing the instant of star 
crossing are thus removed. It is still necessary, 
however, that the operator determine the abso¬ 
lute error of the chronometer very accurately. 
In order to take advantage of the accuracy of 
the Zenith camera, the plate measuring device, 
and the computation procedure, the error in 
timing should be no greater than 0.06 second. 
The observer can compare the chronometer 
with standard radio time signals to one second, 
and then by using the radio chronometer com¬ 
parator measure the fractional error to 0.01 
second. 


42 DESCRIPTION 

The comparator, developed and built by the 
Hughes Aircraft Company, is shown in Fig¬ 
ure 1. Basically it consists of a motor rotating 
at one revolution per second which carries a 
small neon lamp behind a transparent scale 
which is graduated from 0 to 100 around a full 
circle. The lamp is flashed twice each second, 
once by an impulse from the chronometer, and 
once by an impulse from a standard time signal 
received on the radio receiver. The separation 
between the two flashes on the scale gives the 
fractional error of the chronometer in hun¬ 
dredths of a second. 

The radio receiver, which is an integral part 
of the comparator, has to satisfy several re¬ 
quirements. It must be portable and capable of 
operating from self-contained batteries, 110- 
volt a-c or 110-volt d-c power. It should be capa¬ 
ble of receiving Station WWV on one of its four 
frequencies (2.5, 5.0,10.0, and 15.0 megacycles) 
anywhere in the world, and should also be able 
to receive the standard broadcast band and the 
20- to 30-megacycle band. The radio receiver 
which had been used for time comparisons in 
surveying work (Hallicrafter Model S-39) sat¬ 
isfied the frequency range and power source 
requirements very well, but had a high internal 


IAL | 


73 





74 


RADIO CHRONOMETER COMPARATOR 


noise level which made it unable to pick up 
weak signals. Since no other available radio re¬ 
ceiver fitted the requirements as well, it was 
decided to modify the S-39 receiver so as to 
increase the signal-to-noise ratio and thus ob¬ 
tain the desired sensitivity. This was done by 
replacing the S-39 antenna with a standard 
13-ft whip antenna, model AN-29-C. This ne¬ 
cessitated replacing the entire input circuit 
before the grid of the r-f amplifier with a new 
circuit. The impedance of the new antenna was 
calculated and new series-resonant input cir¬ 
cuits designed which could be inductively tuned 
for greater sensitivity. 

Two different types of motors were used to 
rotate the neon light. The first tried was a small 
5-volt d-c motor. Coarse and fine controls were 
provided to adjust the voltage so as to make 
the speed exactly one revolution per second. 
This condition is obtained when the flashes 
from the chronometer or the time signals occur 
at the same point each revolution. One com¬ 
parator was built using a vibrator-type d-c 
motor. The speed of the vibrator was found to 
be essentially independent of voltage and torque 
and showed better speed characteristics than 
the other. There is a problem of electrical noise 


generated by the vibrator contacts which can 
be partially solved by using a separate battery 
for the motor supply. The speed can be con¬ 
trolled by means of a screw which effectively 
varies the vibrator spring stiffness. 

The comparator was tested by the manufac¬ 
turer by comparing a chronometer with time 
signals from Station WWV. It was found that 
comparisons to 0.01 second were possible if 
sufficient care were taken in synchronizing the 
motor speed. One model was also tested in the 
field by being used to time the exposures taken 
with a Zenith camera. The results were of the 
same order of accuracy as those obtained with 
other methods of time comparison. It was not 
felt that sufficient test data had been obtained 
to make possible definite conclusions as to the 
value of the comparator. 211 

The manufacturer feels that the comparator 
is correct in principle, but that a more easily 
synchronized motor is needed. While the modi¬ 
fied receiver has a signal-to-noise ratio about 
10 times better than the original receiver, it is 
still not sensitive enough. They feel that no 
further attempts should be made to improve the 
receiver, but that a completely new receiver 
should be built if more sensitivity is needed. 


^CONFIDENTIAL * 





Chapter 5 

FUEL QUANTITY GAUGES 


51 INTRODUCTION AND SUMMARY 

T his report deals with work done towards 
the development of a reliable and accurate 
fuel quantity gauge for use in aircraft. The 
information desired most by the pilot is not the 
volume of fuel in the tanks, but rather the cruis¬ 
ing radius obtainable with that fuel. This 
cruising radius depends upon the total potential 
heat energy of the fuel which is very closely 
directly proportional to the weight of the fuel 
since the heat of combustion in Btu per pound 
varies less than 1 per cent for the entire range 
of aircraft fuels in use. The indication should 
be accurate to within ±1 per cent of the tank 
capacity and should be unaffected by reasonable 
changes in flying attitude. 

Almost all fuel gauges existing before the 
war measured the tank contents by means of a 
device responding to depth, such as a float or 
hydrostatic unit. The measurement of the depth 
at one point produces a change in indication 
of the gauge with a change in attitude of the 
plane, and, unfortunately, practical considera¬ 
tions usually dictate the placing of the device 
at some point other than the one which would 
make this change a minimum. The hot-wire 
gauge described in Section 5.4 is a depth-meas¬ 
uring device, depending for its operation on the 
difference in the thermal conductivities of the 
liquid and the air and vapor. It is simple in 
principle, and quite a bit of work was done on 
it, but no reliable and accurate gauge was at¬ 
tained. The chief difficulty is that of removing 
spurious effects caused by thermal gradients in 
the liquid. 

Attempts have been made to construct a de¬ 
vice which would actually weigh the amount 
of fuel in the tank, 1 but, while it is possible to 
construct a laboratory model of such a device, 
practical considerations prohibit the actual use 
of it in aircraft. A measurement of the volume 
of the fuel, while not as desirable as a measure¬ 
ment of the mass, would certainly be preferable 
to a simple measurement of the depth at one 
point. Accordingly, work was done on an acous¬ 


tic device which measured the volume of air in 
the tank by measuring the coupling between 
a driver unit and a pickup unit mounted on the 
tank. This device proved unsatisfactory and 
was not carried beyond the experimental stage. 
The chief difficulty was that of removing false 
indications caused by external noise. 

In view of the fact that a Breeze flowmeter 
gives a quite accurate indication of the mass 
rate of fluid flow, an electric frequency meter 
was developed which by measuring that rate 
could be used to measure the quantity of fuel 
remaining in the tank. The frequency meter 
proved satisfactory but was not adopted for use 
as a fuel quantity gauge. 

The best way of getting a measurement of 
the mass of the fuel seems to be by means of 
some kind of capacitor-type fuel gauge. Such 
a gauge depends for its operation upon the 
change in capacity with fuel level of a vertical 
capacitor in the tank. This change occurs be¬ 
cause of the different dielectric constants of 
the fuel and its vapor. An investigation was 
made of the properties of a number of fuels 
to see what effect changes in the temperature 
would have on the calibration. It was found 
that the variation was a linear one which should 
be susceptible to compensation fairly readily. 
A device was developed which made use of the 
change in capacity by using the capacitor as 
part of the tank circuit of a crystal-controlled 
oscillator. The crystal current, read on an r-f 
milliammeter, gave an accurate indication of 
the amount of fuel. Only a rough experimental 
model of this gauge was made, but it seems 
worthy of further development. 


52 ELECTRIC FREQUENCY METER 
AND TACHOMETER 

The operation of the frequency meter 3 is in¬ 
dicated in Figure 1. When the switch S is in 
position 1, the vibrator V, suitably driven either 
mechanically or electrically by the device, the 
frequency of which is to be measured, alter- 




75 




76 


FUEL QUANTITY GAUGES 


nately charges condenser C x from battery E 
through contact K x and discharges it through 
contact K 2 and the shunted ammeter A. The 
average current then is 

1 = NECi, 

where N is the frequency of the vibrator. When 
switch S is in position 2, the current through 
the shunted ammeter will be 



if R x is much larger than the resistance of the 
shunted ammeter. Eliminating E from the 
equations, we have 

n = l. jl. 

/o Cltfl 

The precision of the frequency meter then 
depends on the linearity of the meter and the 
constancy of the values of R x and C x . The varia¬ 
ble shunt R 2 is used to set the meter to the meter 
of the standardizing current 7 0 , thus correcting 
for changes in E. The condenser C 2 is used to 
smooth out the current at low frequencies. 

In the experimental model constructed, A is 
a 0-50 microampere meter; and the other com¬ 
ponents are: E, 12 to 16 volts; R x , 250,000 ohms; 
Ro, 5,000 ohms; C x , 0.1 microfarad; and C 2 , 500 
microfarads. This gives a calibration of 1 mi¬ 
croampere for 1 c if /„ is set at 40 microam¬ 
peres. The time constant of the discharge cir¬ 
cuit is such that charging and discharging of 
condenser C x are essentially completed during 
the times that the vibrator contacts are closed. 

Several types of polarized relays were used 
for the vibrator, but proved unsatisfactory be¬ 
cause of the critical adjustment required. Ac¬ 
cordingly a relay was built from a 0-200 micro¬ 
ampere meter. Spring contact arms were fas¬ 
tened to the coil, and these made contact with 
contacts fastened to the magnet. The relay was 
designed so as to give a wiping eifect between 
the contacts. This wiping tended to prevent 
sticking and bouncing and also cleaned the con¬ 
tact surfaces. This relay was found to be oper¬ 
ated satisfactorily by the output of the Breeze 
flowmeter at frequencies ranging from 1 or 2 
up to 50 c. 


5 3 ACOUSTIC METHOD 

The acoustic volume-measuring device in¬ 
volves applying an oscillating pressure change 
to the air in the tank and measuring the pres¬ 
sure change produced in a receiver connected 
to the tank. Since the amount of coupling be¬ 
tween the driver and the pickup depends on 
volume of air, the output of the pickup device 
should be a measure of the volume of the fuel 
in the tank. 

The first device tried 4 used the same unit for 
both driver and pickup. It was unsatisfactory, 
being able to distinguish between a full tank 
and empty tank, but unable to measure inter¬ 
mediate volumes. 

A device which used small dynamic loud¬ 
speaker units as driver and pickup proved more 
satisfactory. It can be shown 4a that the pickup 
voltage is 


where E 0 is the pickup voltage for the empty 
tank, V f is the volume of the fuel, and V t is the 
volume of the tank. In order to make the in¬ 
strument more sensitive, enough voltage from 
the driver is supplied to the pickup to cancel 
the voltage when the tank is empty. The output 
is measured on a tuned voltmeter. The driver 
used about 0.1 watt of power. 

This device proved more satisfactory than 
the one-unit device, but was not sufficiently ac¬ 
curate (the best accuracy achieved was about 
10 per cent) and had the great disadvantage 
of reacting to external noise. A complete de¬ 
scription of the device, together with sugges¬ 
tions for its improvement, can be found else¬ 
where. 4 Because of the difficulties as to size and 
complexity of equipment needed to make a sat¬ 
isfactory acoustic gauge, further work was dis¬ 
continued. 


5 4 HOT-WIRE METHOD 

The hot-wire gauge depends for its operation 
on the differing thermal conductivities of the 
liquid fuel and of the air and vapor above it. 






HOT-WIRE METHOD 


77 


If a vertical resistance wire in the fuel tank is 
heated in some manner, the fraction of the wire 
in the liquid will be cooler, with a lower re¬ 
sistance per unit length, than the fraction above 
the liquid. The resistance of the wire, then, 
gives a measure of the depth of the liquid. Pre¬ 
liminary development of the hot-wire gauge 
was undertaken at Johns Hopkins University 511 
using a Wheatstone bridge arrangement, but 


Since the two sides of the network are the same, 
they will carry the same current, and we have 

e _ iR 3 — iR<i _ x 

E ~ iR 3 - iRi ~ 77' 

It is assumed that the resistances of the devices 
used to measure e and E are very large com¬ 
pared to the resistances of network branches. 



Figure 1. Schematic electric circuit of frequency 
meter. 


it was found that the simple circuit used was 
sensitive to changes in both pressure and tem¬ 
perature. Further work was carried on at the 
laboratories of Joseph Rozek, 5b where a simple 
method was developed which would automati¬ 
cally compensate for changes in the thermal 
conductivity of the air and vapor caused by 
changes in either the pressure or temperature 
or both. 

Figure 2 gives the basic electric circuit for 
the gauge. R ,, R 2 , and R are identical resistance 
wires with R x being wholly within the liquid, 
R 3 wholly above the liquid, and R 2 being the 
vertical wire the resistance of which changes 
with the depth of the liquid. A simple derivation 
gives the following expression for the fraction 
of the wire immersed in the liquid: 

x _ R 3 — R 2 

L~ R 3 - Ri 

The ratio network shown in Figure 3 reduces 
the measurement of this ratio to the measure¬ 
ment of two voltages. Each of the three resist¬ 
ances is duplicated by an identical resistance, 
and the six resistances are connected as shown. 



Figure 2. Basic circuit of hot-wire fuel gauge. 


A number of different models were con¬ 
structed, and a full description of them together 
with the results obtained may be found else¬ 
where. 55 Most of the gauges were constructed 
so that the network current was the heating 
current, although the use of separate heating 
wires was tried. The chief precaution to be ob- 


1 




Figure 3. Ratio network of hot-wire fuel gauge. 

served is to have the geometry of the indicating 
elements and the vapor compensating elements 
identical so as to cancel out the effects of 
thermal differentials. This can be done in a 
laboratory model, but the difficulties involved 
in doing it for a gauge suitable for use in air- 


CO-VFIDENTIAL 


f 





















































78 


FUEL QUANTITY GAUGES 


craft have not been solved. The extreme sim¬ 
plicity of this type of gauge would seem to war¬ 
rant its further development. It does, however, 
suffer the additional difficulty of measuring the 
depth at one point, rather than the mass of the 
fuel. 


55 CAPACITY METHODS 

501 Introduction 

The basic principle of operation of a capacity- 
type fuel gauge is the change with liquid level 
of the capacity of a condenser with vertical 
plates mounted in the fuel tank. This change 
occurs because the dielectric constant of the 
fuel is about 2, as compared with the value of 1 
for the air and vapor. This principle had been 
applied in some British gauges, 1 ' 2 and some 
work done at the Royal Aircraft Establishment 1 
indicated the feasibility of designing a con¬ 
denser system, the capacity of which would give 
an accurate measurement of the mass of the 
fuel, regardless of any normal changes in atti¬ 
tude of the plane. The condenser systems would, 
of course, be different for different aircraft 
tanks, but this presents no particular problem. 
Suggested systems for several types of aircraft 
are given in the British report. 1 One important 
question is the effect of temperature upon the 
accuracy of such a gauge. This was investigated 
by the Gulf Research and Development Com¬ 
pany, 6 and the work is described in the next 
section. 


Tests of Different Fuels 

A simple theoretical argument 08 shows that 
the indication of a capacity gauge will be given 
by 

/ = ^M(S-l) 

P 

where 7 is the indication, M is the mass, 2 the 
dielectric constant, P the density of the fuel, 
and A is a constant depending on the tank 
and condenser geometry. The temperature de¬ 
pendence of the gauge indication, then, will be 


determined by the temperature variation of the 
quantity (2 — 1 )/ P . 

Measurements were made on four different 
fuels: a standard commercial fuel, and three 
synthetic fuels blended so as to give (1) a typi¬ 
cal fuel, (2) an aromatic-type fuel, and (3) a 
paraffinic-type fuel. All the fuels meet the speci- 



Figure 4. Variation of (2-1) /p with tempera¬ 
ture for four aircraft engine fuels. 


fications for aircraft fuels and are thought to 
represent the maximum range which might be 
encountered. The detailed specifications of the 
four fuels may be found elsewhere. 6b 

The results of the investigation are given in 
Figure 4. Here the quantity (2 — 1) / P for the 
four fuels is plotted against the temperature. 



Figure 5. Per cent error in capacity versus tem¬ 
perature for four aircraft engine fuels. 


Figure 5 shows the same data converted to per 
cent error in indication, taking the synthetic 
typical fuel at 68 F as correct. There are two 
important conclusions to be drawn. The first is 
that the variation between different fuels can 
be much larger than the temperature variation 



















































CAPACITY METHODS 


79 


for a single fuel. This means that some pro¬ 
vision must be made for adjusting the gauge to 
a particular fuel. However, this variation is 
not as bad as it appears because actual fuels 
encountered would probably range between the 
commercial fuel and the synthetic typical fuel. 
The second conclusion is that the variation with 
temperature is a linear one, and as such should 
be susceptible of being compensated for by 
some fairly simple temperature-dependent elec¬ 
tric device. 

The effect of contaminants apt to be encoun¬ 
tered was studied, and the conclusion reached 
was that they would not produce errors if pro¬ 
vision was made to prevent their collecting at 
the bottom of the condensers. 


5 3,3 Oscillator Method 

A simple capacity-type gauge was constructed 
in which the condenser was used as part of the 
tank circuit of a crystal-controlled oscillator. 50 
The indication was the crystal current as read 
on a hot-wire milliammeter. The electric circuit 
of this gauge is shown in Figure 6. The con¬ 
denser is a brass tube with a central brass 
cylinder and is inductively connected to the 
plate circuit to eliminate any d-c voltages in 
the fuel tank. The laboratory model of this 
gauge proved quite satisfactory except that a 
stabilized plate supply is necessary. It is, how¬ 
ever, very similar to the British Waymouth 


gauge 1 and would suffer from the same disad¬ 
vantages. These are difficulties with radio inter¬ 
ference and the effect of the capacity of the 



pacity gauge. 

connecting cable. The latter makes it necessary 
to calibrate for each location, or length of cable, 
and increases the variation with temperature. 


CONFIDENTIAL f 





























































Chapter 6 

COMBUSTION EFFICIENCY INDICATOR FOR NAVAL VESSELS 

By F. L. Yost a 


61 INTRODUCTION 

O N board ship, the fireman’s first task is to 
maintain steam pressure at the predeter¬ 
mined value at which the turbines are designed 
to operate most efficiently. The second task is to 
generate steam in the most efficient manner with¬ 
out betraying the position of the ship by smoke 
or haze. It is generally conceded that the most 
efficient combustion at a given oil-burning rate 
occurs when a slight haze or light wisps of 
brown smoke leave the top of the stack. This 
operating condition, known as “trace smoke,” 
is not permissible aboard ship; therefore, suffi¬ 
cient air must be used for combustion so that 
smoke or haze is just eliminated. When there 
is insufficient air black smoke results, and when 
excessive quantities of air are used a white 
smoke results. Operation must occur between 
these limits. The overall boiler efficiency at 
white smoke, however, may be as much as 10 
per cent less than it is at a trace of brown 
smoke, the condition for optimum combustion. 

The proper procedure for adjusting the air 
rate to give the most efficient permissible com¬ 
bustion after lighting off a burner is to decrease 
the air pressure gradually and to observe the 
stack through a fireroom periscope until a 
slight haze can be distinguished by an experi¬ 
enced observer. When the haze appears, the air 
pressure is increased by a tenth of an inch of 
water, or less, to just eliminate the haze. Such 
adjustment cannot be made rapidly since suffi¬ 
cient time must be allowed between each change 
in air pressure to permit the furnace to re¬ 
spond. Since the criterion of operation is “no 
smoke,” it is easy to play safe and use ample 
air, particularly if the oil pressure is varied 
from time to time to maintain steam pressure. 

The appearance of a trace smoke as an indi¬ 
cation of the proper air pressure for most effi¬ 
cient combustion is not a guarantee that the 
greatest efficiency is being realized. There are 
a Technical Aide, Division 17, NDRC. 


a number of factors which affect the efficiency 
of combustion before a trace smoke appears. 
The most satisfactory and practical single 
measurement which can be made to determine 
combustion efficiency is flue gas analysis for 
carbon dioxide. This was believed to be true 
prior to the study reported here and was one 
of the conclusions of this study. Prior to this 
work, the Navy had adopted a Ranarex carbon 
dioxide recorder [RR] but difficulties (see Sec¬ 
tion 6.4.2) connected with it caused it to be 
abandoned. 

In the early days of Section D-3 of NDRC, it 
was proposed that a project be set up to investi¬ 
gate the feasibility of providing an acceptable 
combustion efficiency indicator for naval boil¬ 
ers. It was hoped that, by a careful control of 
boiler efficiencies, a fuel saving of as much as 6 
per cent might be effected, and the cruising 
radii of ships might thereby be increased. 


62 MILITARY REQUIREMENTS 

The basic military requirement in the devel¬ 
opment of a device was that it indicate fairly 
accurately the efficiency of combustion in a 
naval oil-fired boiler. There were other require¬ 
ments which were desirable. The instrument 
should be simple. It should have a large indicat¬ 
ing dial. It should have practically no lag in fol¬ 
lowing changes in firing conditions. There were 
still other requirements which were necessary 
from a practical viewpoint. The apparatus 
should require very infrequent attention to 
maintain it in operation. Any necessary serv¬ 
icing should be of such nature that it could be 
performed by enlisted personnel. 


6 3 SUMMARY OF DEVELOPMENT 

The work on this project, which proceeded 
along a number of different lines, 18 was done by 



80 




DESCRIPTION AND TECHNICAL INFORMATION 


81 


the Towne Scientific School of the University of 
Pennsylvania. 

Through the cooperation of an oil-burning 
school established at the Naval Boiler and Tur¬ 
bine Laboratory of the United States Navy 
Yard, Philadelphia, Pennsylvania, it was pos¬ 
sible to observe shipboard fireroom practice. The 
personnel of this project spent several weeks 
observing demonstrations of the recommended 
manner of firing boilers, which made it possible 
to learn some of the numerous factors which 
affect combustion efficiency. In certain cases, 
it was possible to make experimental measure¬ 
ments to determine the magnitude of the effect 
of these factors. Some of the conclusions 
reached in this study are given in Section 6.4. 
The main value of this investigation was that it 
gave a necessary background of information 
concerning standard practice in boiler firing— 
a fund of information which could not have 
been obtained in any other way. 

Early in this investigation, it was learned 
that the Naval Research Laboratory had done 
some work which seemed to indicate that flame 
brightness might serve as a measure of com¬ 
bustion efficiency. This work was reviewed, and 
additional tests were run. 8a It was concluded 
that flame brightness was not a suitable indi¬ 
cation of combustion efficiency. 

Since it had been thought all along that analy¬ 
sis of the flue gases for carbon dioxide would give 
the best indication of combustion efficiency, three 
commercially available types of carbon dioxide 
indicator were tested, 8b each working on a differ¬ 
ent principle. The type which most nearly met 
the requirements was determined, and methods 
were suggested for increasing its suitability for 
naval use. 8c These alterations would not have 
increased the simplicity of the instrument, nor 
would they have lowered the amount of atten¬ 
tion it required. A general conclusion of this 
study was that, since boiler efficiency depends 
on a number of factors, some independent and 
some interdependent, it is reasonably safe to 
say that no rugged simple indicator of combus¬ 
tion efficiency can be devised depending on the 
measurement of a single parameter. 

It does seem that the firing of naval boilers 
should be under instrument control to assure 
maximal efficiency combined with freedom from 


smoke dangers. The instruments which could 
be devised for this purpose are necessarily com¬ 
plex and involve the measurement of more than 
one variable so that the attention of an engineer 
officer is necessary. The vital importance of 
boiler efficiency in the operation of naval ves¬ 
sels seems to justify fully the employment of 
skilled technical officer supervision. 


64 DESCRIPTION AND TECHNICAL 
INFORMATION 

6,4-1 Study of Firing Technique 

The results of observations at the Naval 
Boiler and Turbine Laboratory may be sum¬ 
marized as follows. 

1. Several of the numerous factors affecting 
combustion efficiency can be eliminated as op¬ 
erating variables by properly adjusting them 
and holding them constant. Among these are 
fuel oil viscosity and fuel oil quality. 

2. Other variables limit the maximum com¬ 
bustion efficiency which can be realized under 
a given rate of generating steam. There is little 
variation practical for these factors which in¬ 
clude sprayer plate size, type of nozzle, fuel oil 
pressure, and number of burners in operation. 

3. There are several factors which, at a 
given steaming rate, can be varied by the fire¬ 
man to improve or change the combustion effi¬ 
ciency of the burner. Among these are register 
opening, burner withdrawal, and air pressure. 
The first two are usually set for an atomizer of 
given size. For maximum efficiency, the air 
pressure should be held to a minimum without 
generating smoke. It is in this respect that the 
greatest improvement can be made. 

4. Complete automatic control of boiler firing 
would eliminate the need for a combustion effi¬ 
ciency indicator except as a check upon the suc¬ 
cessful operation of the automatic control in¬ 
struments. 


6,4,2 Carbon Dioxide Recorders 

Analysis of flue gases for carbon dioxide 
gives the best indication of combustion effi- 



82 


COMBUSTION EFFICIENCY INDICATOR FOR NAVAL VESSELS 


ciency, even though this method has its draw¬ 
backs. A fixed value for the percentage of car¬ 
bon dioxide cannot be specified as a criterion of 
maximal combustion efficiency since other fac¬ 
tors, such as steaming rate, limit the maximum 
percentage which can be obtained in the flue 
gases without obtaining smoke. Flue gas analy¬ 
sis varies with the fuel or oil being used. Fur¬ 
thermore, flue gas analysis does not indicate 
what is happening at the burner until the com¬ 
bustion products reach the point where a sample 
is being taken. Thus, before an indication oc¬ 
curs, there is a lag equal to the time required 
for the combustion products to travel through 
the furnace. It would be preferable to have an 
indicator respond when a valve is turned or an 
air register is opened. 

Although its limitations are clearly recog¬ 
nized, no better practical method of measuring 
combustion efficiency has been found than flue 
gas analysis. Accordingly, considerable time 
was spent in studying devices which could be 
used for this purpose. 8 As stated in Section 6.3, 
three commercial carbon dioxide recorders were 
installed and tested on a horizontal return-tube 
boiler. They were (1) a Leeds and Northrup 
recorder [LNR], a thermal conductivity or elec¬ 
trical type; (2) a Hays recorder [HR], an auto¬ 
matic orsat or chemical type; and (3) a Rana- 
rex recorder [RR], a mechanical type. (An 
orsat is a portable gas analysis apparatus which 
consists of a measuring buret and three or four 
gas absorption pipets connected to a manifold.) 
Photographs of the test installations have been 
published. 8 

The LNR uses the thermal conductivity of the 
flue gas to give the carbon dioxide content of the 
gas. This conductivity is measured by means of 
a calibrated electric resistance with a large 
thermal coefficient of resistance. The recorder 
and flue gas analyzer assembly consists of a 
sampling device and lines bringing the flue gas 
to the analyzing cell which is mounted as near 
to the sampling point as possible. The sample is 
drawn into the apparatus by an aspirator op¬ 
erated by water or compressed air. The analysis 
is transmitted electrically to a micromax indi¬ 
cator and recorder. 

The HR is a mechanical form of hand orsat 
used for flue gas analysis. The pumping action 


of water is used to pass a measured quantity of 
gas over caustic solution. A pneumatic device 
transmits the flue gas analysis to a chart. The 
HR operates intermittently. Samples are taken 
about every 2 minutes, although flue gas is con¬ 
tinuously aspirated through the instrument, by¬ 
passing the analyzing section when an analysis 
is in progress. The instrument consists of two 
parts: an analyzing cell near the point of 
sampling and a recorder located within easy 
sight of the fireman. 

The RR is mechanical in nature. Two motor- 
driven fans blow separate streams of air and 
flue gas against two other fans which are cou¬ 
pled in such a way that the difference in the 
torques on the two receiving fans can be ob¬ 
served. This difference in the torques is propor¬ 
tional to the difference in gas densities which, 
in turn, is proportional to the gas compositions. 

Both the LNR and HR were difficult to cali¬ 
brate, but, once calibrated, they retained the 
calibration very well. The RR was easier to cali¬ 
brate, but needed frequent recalibration. The 
RR had the shortest response time. The LNR 
had the longest response time, which was be¬ 
tween 2 and 3 minutes. 

The reliabilities of the instruments were de¬ 
termined daily by comparison with an orsat 
analysis. 8 Since the original calibration of each 
instrument was subject to an unknown error, 
the average of all daily deviations was taken to 
be the calibration error. The residuals, defined 
as deviation minus mean deviation, were con¬ 
sidered to be a measure of the accuracy of the 
instrument. The reliability was defined as the 
average deviation of a single observation from 
the corrected mean. 

The calibration error of the HR was found 
to be —0.5 per cent CCL, and its reliability 
±0.34 per cent C0 2 . The calibration error for 
the LNR was —0.3 per cent, and its reliability 
was ±0.44 per cent. The calibration error for 
the RR canceled out statistically over a period 
of time (possibly caused by the frequent cali¬ 
brations necessary), and its reliability was only 
±0.96 per cent. 

Many of the features of all three of these re¬ 
corders are mechanical in nature and require 
the usual maintenance of oiling, greasing, clean¬ 
ing, and similar care. Maintenance peculiar to 




DESCRIPTION AND TECHNICAL INFORMATION 


83 


carbon dioxide recorders is the cleaning of stack 
filters every few months and weekly replacement 
or cleaning of secondary filters. In addition, the 
LNR saturating chamber must be refilled once 
or twice a week. The thermal-conductivity cell 
requires periodic cleaning every three or six 
months, depending on the cleanness of the flue 
gas. In the HR, caustic solution must be re¬ 
placed every six months while the “tattler jar” 
must be refilled with water every two or three 
days. Certain hard-rubber capillaries should be 
cleaned every month or two. The RR saturating 
chambers require filling once a week. A daily 
zero check is also necessary. The internal mech¬ 
anism, including such parts as fans and fan 
shafts, requires complete cleaning once or twice 
a year. 

The LNR is a complicated electric instrument 
with a sensitive galvanometer. The analyzing 
cell is made of glass and is consequently fragile. 
Servicing the LNR requires the aid of a quali¬ 
fied instrument man. The HR requires a large 
quantity of water for its operation. A level 
mounting is essential for accurate analysis. 
Caustic solution in the hands of careless or in¬ 
experienced men might be dangerous. The RR 
is rugged and compact. It reads only in a level 
vertical position. Being mechanical in principle, 
it can be serviced by an intelligent or experi¬ 
enced mechanic. 

Because of special considerations involved in 
the naval application of a carbon dioxide re¬ 
corder, such as speed of response, compactness 
and simplicity, pitch and roll of a ship, vibra¬ 
tion and shock, maintenance and servicing, and 
reliability, it was decided that the RR was the 
most promising. 

In its available form, the RR has a number of 
undesirable features. Insufficient power is de¬ 
veloped by the measuring device to position an 
indicator and recorder. The belt drive on the 
pulleys of both fans may slip so that both fans 
may not have the same speed of revolution. The 
bearing for the shaft of the impulse fan permits 
a cantilever action which may affect the free¬ 
dom of rotation of the fan. There is no guaran¬ 
tee that the flue gas and air are at the same 
temperature, pressure, and moisture content 
conditions essential for proper operation. There 
is no provision to discharge water from saturat¬ 


ing chambers which in time may become 
strongly acidic. There are no sight glasses to 
indicate when the water levels in saturating 
chambers are getting low. 

Auxiliary apparatus was designed for the RR 
to give the desired heat transfer between flue 
gas and air and to insure saturation of both air 
and flue gas. Tests showed that a slight differ¬ 
ence in pressure could still exist between the air 
and flue gas. It was finally decided that the 
auxiliary apparatus was not suitable for naval 
use. Several features of the RR which might be 
modified for better results are: 

1. A positive drive for both impeller fans to 
insure constant and equal speed would be de¬ 
sirable. This could be accomplished by mounting 
the fans on the same shaft, by using a chain 
drive, or by using two synchronous motors. 

2. A more powerful fan-motor system could 
be used to draw larger gas quantities for test 
and thus to reduce the time of response. 

3. The usual indicator and recorder system 
could be replaced with an auxiliary unit by 
means of which the small differential torque 
developed by the impulse fans could be used to 
transmit the reading to a more powerful indi¬ 
cating and recording system. This would free 
the analyzing system of a drag which may con¬ 
tribute to its inaccuracies. 

4. The design of the bearing and shaft ar¬ 
rangement in the instrument might be im¬ 
proved. 

As far as carbon dioxide recorders were con¬ 
cerned, this project made the above comparison 
of three commercially available types and sug¬ 
gested improvements which might be made on 
the one which appeared most suitable for naval 
use. No new instrument for measuring com¬ 
bustion efficiency aboard naval vessels was de¬ 
veloped. It was believed, however, that, if the 
RR were rebuilt as suggested above, an instru¬ 
ment acceptable to the Navy might be pro¬ 
duced. It was believed also that further work 
should be conducted along the lines of these 
studies. Modern engineering science can cer¬ 
tainly produce instrument controls for oil-fired 
boilers capable of maintaining an operating effi¬ 
ciency superior to that achieved through rule- 
of-thumb methods depending on prejudices and 
opinions of naval enlisted personnel. 



84 


COMBUSTION EFFICIENCY INDICATOR FOR NAVAL VESSELS 


Flame Brightness as a Test of 
Combustion Efficiency 

Data taken by the Naval Research Labora¬ 
tory, in the course of unrelated work, showed 
that flame brightness went through a maximum 
close to optimum firing condition for each firing 
rate. Maximum brightness occurred further in 
the region of smoke at the higher firing rates. 
The brightness peak varied with firing rate and 
was not very marked at the lowest firing rate. 

The original work was done with a MacBeth 
illuminator, but flickering flame made it ex¬ 
tremely difficult to make readings. Measure¬ 
ments were repeated with a General Electric 
exposure meter protected with a water filter. 

Two sets of readings were taken at varying 
conditions of excess air to obtain a qualitative 
indication of the relation between flame bright¬ 
ness and excess air. A third set of readings was 
taken with simultaneous determinations of car¬ 
bon dioxide in the flue gas. There was no per¬ 
ceptible maximum of brightness up to the point 
of trace smoke. It was concluded that, while 
this method had originally looked very promis¬ 
ing, it was unsuitable for use. 


644 Steam Flow-Oil Flow as an 

Indication of Combustion Efficiency 

The overall purpose of boiler operation is to 
generate steam at a predetermined temperature 
and pressure. Accordingly, the overall efficiency 
of the installation is measured by the pounds of 
steam generated per pound of oil. It was there¬ 
fore thought that measurement of this ratio 
might be used to indicate overall efficiency. The 
complete data for 11 different boilers tested by 
the Naval Turbine and Boiler Laboratory in the 
period from February 1937 to October 1941 
were examined, calculated, and plotted to de¬ 
termine whether a general correlation of steam 
flow and oil flow was possible. Examination of 
the curves showed no general correlation. An 
instrument employing this principle would have 
to be calibrated for every type of boiler on 
which it was to be used, the calibration to be 
based on test data obtained at the Naval Tur¬ 
bine and Boiler Laboratory. When this work 
was being done, 50 per cent of the boilers in use 
had not been tested at that laboratory. There 
were, in addition, other difficulties which would 
have been associated with such a method. 








PART II 


SOUND TRANSMISSION AND INSTRUMENTATION 


C0NFIDENTIA1 






Chapter 7 

ULTRASONIC SIGNALING 


By Harold K. Schilling 


71 INTRODUCTION 

T his project was established to investigate 
the possibilities of ultrasonic signaling and 
communication. For temperate zone conditions, 
the investigation was conducted at State Col¬ 
lege, Pennsylvania, 1 in the spring of 1944, both 
in open country and in forests. Later, an expedi¬ 
tion of six men from the Penn State College 
project studied the effects of tropical conditions 
in Panama- 3 for approximately two months 
during the rainy season. 

While in Panama, the Penn State College 
group was closely associated with a similar ex¬ 
pedition from Rutgers University which was 
investigating various aspects of audible jungle 
noises (see Chapter 8). Obviously, both proj¬ 
ects had one common factor, namely, the detec¬ 
tion of the aerial vibrations that existed under 
various conditions in jungle terrain. In one 
case, however, interest was focused on the in¬ 
audible region of the sound spectrum, while in 
the other it was the audible region that was of 
primary interest. It was inevitable, therefore, 
that the two expeditions should collaborate and 
profit by the mutual assistance received on 
problems of common interest. 

The researches on ultrasonic signaling pro¬ 
ceeded along two lines: (1) the design and con¬ 
struction of suitable equipment, and (2) the 
determination of the possible range and relia¬ 
bility of ultrasonic signaling under various con¬ 
ditions of weather and terrain, with special 
emphasis upon jungle conditions in the tropics. 

72 EQUIPMENT 

Sources 

Only whistles were used as sources because 
from the viewpoint of size, weight, and simplic¬ 
ity of operation they seemed most suitable for 
use by the Army, as well as for research pur¬ 
poses, in dense tropical jungles. 


An empirical study 1 was carried out to dis¬ 
cover (1) what determines the intensity and 
frequency of their output, (2) what determines 
their suitability for mouthblowing, (3) what 
methods of actuating them might be useful un¬ 
der field conditions, and (4) how to minimize 
or eliminate their audible hiss and transients. 
The resulting information has led to the im¬ 
provement of old whistles and the development 
of two new kinds. 3 

The highest signal intensity level attained by 
a mouthblown whistle was 110 db at a distance 
of 1 ft. This required an airflow of 500 cu cm 
per sec. The output was about 0.1 watt, the effi¬ 
ciency approximately 5 per cent. Using air from 
high pressure tanks, the corresponding figures 
are 130 db at 1 ft, 4,000 cu cm per sec, 10 watts, 
3 per cent. 

Receivers 

No attempt was made to design small re¬ 
ceivers suitable for use by the individual soldier, 
that task having been assigned elsewhere. 
Rather, the object was to produce research 
equipment which could detect signals at the 
greatest possible distance and maintain its op¬ 
erating characteristics under the most unfavor¬ 
able field conditions. 

Five portable, sharply selective receivers 
were built, covering the frequency range from 
7 to 30 kc. All employed Western Electric 640-A 
condenser microphones. Four had resistance- 
coupled amplifiers, and one a heterodyne circuit. 
Between 17 and 27 kc all were capable of meas¬ 
uring intensity levels from 25 to 35 db up to 
approximately 140 db above 10~ 16 watts per sq 
cm. 

Auxiliary apparatus included special test in¬ 
struments used in the field in checking calibra¬ 
tions and locating troubles. 

Parabolic Reflectors 

The effectiveness of using parabolic reflectors 
of various diameters up to 12 in. in conjunction 


CONFIDENTIAL f 


87 




88 


ULTRASONIC SIGNALING 


with both sources and receivers was investi¬ 
gated. In unforested regions, the largest made 
available about 40 more db and in forests about 
15 db. The resulting increase of directionality 
was not large enough to be a handicap in sig¬ 
naling. 

Meteorological and 
Micrometeorological Equipment 3 

For large-scale meteorological measurements 
standard instruments were used. For micro- 
meteorological measurements the following spe¬ 
cial portable apparatus was built: (1) four sen¬ 
sitive resistance thermometers using nickel 
wires 0.0005 in. in diameter, (2) four sensitive 
hot-wire anemometers using platinum wires 
0.0004 in. in diameter, (3) two direct-reading 
temperature-difference meters, (4) two direct- 
reading velocity-difference meters, and (5) 
auxiliary equipment, such as portable and col¬ 
lapsible masts. 

Tropic Proofing 3 

All equipment was carefully tropic proofed. 
This and special precautions taken in the field 
and at headquarters were sufficient to prevent 
any failure of apparatus due to adverse tropical 
conditions. 

7 3 TRANSMISSION MEASUREMENTS 

Transmission studies were of two types: (1) 
direct measurements of signaling ranges, and 
(2) investigations of propagation phenomena 
and related factors determining or affecting 
ranges. 

Range Measurements 

Signaling distances were measured for dif¬ 
ferent frequencies, over many types of terrain, 
at various heights above the ground, in open 
country as well as in forests of different densi¬ 
ties, under different weather conditions, at vari¬ 
ous times of day and night, both in the temper¬ 
ate and tropic zones. 

These measurements revealed that for a 
given terrain there is no single value of the sig¬ 
naling range. Thus one might one day be able 
to signal 400 ft, and on another find it impos¬ 
sible to signal more than half that far—at the 


same place and with the same apparatus. Also, 
ranges often vary greatly in length within short 
time intervals. Though the intensity at the 
source may be constant, the received signal fre¬ 
quently fluctuates in intensity as much as 20 db 
within a few minutes, or even seconds. Conse¬ 
quently, near the end of a range signals often 
fade out and reappear quite unpredictably. 

The experimental procedure was to deter¬ 
mine the absolute intensity level first 1 ft from 
the source and then at increasingly larger dis¬ 
tances until the signal could no longer be de- 



20 40 60 80 100 200 400 600 800 


DISTANCE IN FEET 

Figure 1. Transmission curves for unforested 

areas, 17 kc. 

tected. The transmission losses in decibels were 
then computed and plotted, as negative ordi¬ 
nates, against the corresponding distances, as 
abscissas, on semilog paper. 

Typical transmission curves obtained in that 
manner for unforested areas are depicted in 
Figure 1. Obviously, a maximum signaling dis¬ 
tance depends upon two factors: (1) the char¬ 
acteristics of the apparatus, and (2) the 
properties and condition of the propagating 
medium. Thus, the equipment limits the number 
of decibels one can “work with,” while the 
medium determines the distance within which 
that much loss occurs. A transmission curve de¬ 
picts the latter. 

Such considerations have suggested the use 
of the term “n db range” to denote the distance 
within which a signal suffers a transmission 
loss of n decibels relative to its intensity at 1 ft 
from the source. Thus, when curve A (Figure 
1) was obtained, a 60 db range was 210 ft, and 
an 80 db range was 410 ft. 

Figure 1 may be regarded as representing the 
overall possibilities of signaling for the particu- 

































TRANSMISSION MEASUREMENTS 


89 


lar frequency of 17.5 kc in open country. Curves 
A and B show respectively the most and the 
least that can be expected. Thus apparatus ca¬ 
pable of handling a transmission loss of 100 db 
should under the worst conditions yield a range 



Figure 2. A curves: (top) straight, typical of 
open air with absorption but without scattering; 
(middle) curved, as in jungles or in air which is 
both absorbing and scattering; (bottom) broken, 
indicating “zone of silence.” 

of at least 98 ft and at most 710 ft. The area be¬ 
tween curves A and C represents the spread of 
ranges in Panama when both source and re¬ 
ceiver were 3 to 5 ft above the ground. Region 
A to D indicates the spread in Pennsylvania for 
the same heights. Curves D, E, F, and B respec¬ 
tively depict the practical lower limits for 
ranges at the heights of 60, 30, 10, and 3 in., 
while curve A indicates the upper limit for all 
heights. 


It is impossible to speak of typical transmis¬ 
sion curves for jungles in general. Not only is 
the rate of attenuation different for jungles of 
different densities, but also that rate changes 
with distance in various ways. It can be said, 
however, that in only few jungles would the 
ranges be as long as those indicated by curve C, 
and in many the ranges are less than half as 
long as those given by curve B. 

Study of Transmission Phenomena 

In open unforested areas, when there are no 
large-scale temperature or wind gradients, the 
variation of signal intensity with distance can 
usually be explained simply in terms of the in¬ 
verse square law (a whistle being essentially a 
point source) and a negative exponential law 
(the air having an absorption coefficient for 
ultrasonic energy). 

This is indicated by the rectilinearity of so- 
called A curves, 3 illustrated by curve A, Figure 
2. Such a curve is obtained by subtracting the 
transmission losses due to divergence (given by 
the dashed line G in Figure 1) from the total 
transmission losses (depicted by transmission 
curves such as A, B, etc., in Figure 1) and then 
plotting the difference in decibels (that differ¬ 
ence being due to the medium and terrain and 
therefore referred to in the figure as physical 
transmission loss) against distance on rec¬ 
tangular coordinate paper. 

The slope of such a derived A curve, when it 
is rectilinear, equals the absorption coefficient 
of the air in decibels per foot. The values of the 
coefficients obtained in this manner are con¬ 
sistent with those pbtained by other workers by 
other methods. 

In a forest a A curve is always bent (see curve 
B, Figure 2), i.e., has one or more “knees” in it. 
This is due to scattering in the medium, say, by 
leaves or branches. A theory of absorbing scat¬ 
tering media has been developed which rather 
successfully explains such A curves and yields 
a method of computing separate effects of scat¬ 
tering and absorption. 

At times the air itself (at locations where 
there are no “foreign” solid bodies, such as 
leaves) is a scattering as well as absorbing 
medium. Here again, when correction is made 
for scattering, the absorption coefficients ob- 


GQNFIDENTIAL 










90 


ULTRASONIC SIGNALING 


tained are consistent with values obtained by- 
others. 

When there are large-scale temperature 
lapses or opposing winds the A curves are 
broken, i.e., have discontinuities as illustrated 
by curve C, Figure 2. These are due to the 
presence of zones of silence in which the rate 
of attenuation is different from that obtained 
outside such regions. The appearance, evolu¬ 
tion, and disappearance of such zones have re¬ 
peatedly been observed both acoustically and 
micrometeorologically through complete 24-hour 
periods. 3 

Three types of intensity fluctuations, two of 
them periodic and one random, have been recog¬ 
nized and correlated with related micrometeor- 
ological phenomena. 

Diffraction 

The possibility of ultrasonic signaling around 
obstacles is of considerable importance from the 
military point of view. Thus, if because of sharp 
acoustic shadows it were impossible to signal 
to points in back of large trees, or over barri¬ 
cades, or into trenches, the usefulness of such 
signaling would be greatly impaired. 

Simple diffraction theory suggests that for 
waves 1 or 2 cm in length most bodies of ordi¬ 
nary size should cast rather sharp shadows. On 
the other hand, in many practical situations, 
conditions are such that simple theory does not 
seem entirely applicable. 

Experimental investigation 3 shows that: (1) 
in typical jungles, intense ultrasonic shadows 
are almost nonexistent for frequencies near 20 
kc; (2) in the open, when larger distances are 
involved, obstacles present no serious difficulty. 
Thus, in the open country, signaling over a dis¬ 
tance of several hundred feet would often be 
about as effective whether a 5 ft or 6 ft high 
wall were halfway between source and receiver 
or not. In such cases, favorable gradients are 
helpful. (3) For short-range signaling in the 
open, simple theory predicts fairly well what 
may be expected. 

7 4 AMBIENT NOISE 

The intensity and spectral distribution of 
outdoor background noise, both in the audible 


and ultrasonic frequency ranges, and the diur¬ 
nal cyclic variation of such noise were meas¬ 
ured in Panama 3 at many locations. The jungles 
of Panama during the rainy season were found 
to be no noisier than the forests of Pennsylvania 
during the summer and early fall. 

75 SUMMARY OF RESULTS AND 
CONCLUSIONS 

1. Ultrasonic signaling is feasible over rela¬ 
tively short distances only. The absorption in 
the air is so great as to preclude the possibility 
of materially increasing the longest ranges re¬ 
ported herein through improvement of sources 
or receivers. 

2. Experience suggests that it should be pos¬ 
sible to develop small, portable equipment, in¬ 
cluding mouthblown whistles and receivers 
weighing not more than 3 or 4 lb, capable of 
signaling over 90 db ranges. 

3. In open country, without obstructions, 90 
db ranges at approximately 20 kc are rarely 
longer than 500 ft. 

4. In jungles 90 db ranges are never longer 
than 300 ft. In an average Panamanian jungle 
a 90 db range is approximately 200 ft. In thick 
underbrush such a range is not more than 75 
ft. In dense tropical grass it is still less. 

5. Ranges decrease with increasing fre¬ 
quency. For the frequency of 29 kc ranges are 
approximately 40 per cent shorter than those 
for 20 kc. 

6. In open country ranges usually increase 
rapidly with increasing height above the 
ground up to 4 or 5 ft and then only slightly up 
to 10 ft. For some weather conditions ranges 3 
in. from the ground may be less than 25 per cent 
of those at 5 ft. Only under exceptional condi¬ 
tions are ranges nearly independent of height. 

7. In forests ranges are much less dependent 
upon height. In dense jungles ranges are essen¬ 
tially independent of height. 

8. Weather conditions most favorable to 
steady and long-range signaling are: (1) no 
wind; (2) absence of vertical temperature 
lapses, and (3) cloudiness and rain. Usually 
conditions are much more steady and uniform 
in forests than out in the open. Ordinarily, 
nighttime is more favorable than daytime. 


CONFIDENTIAL * 





SUMMARY OF RESULTS AND CONCLUSIONS 


91 


9. The ultrasonic picture in Panama is much 
like that in Pennsylvania. Similar ranges were 
obtained. The main difference is that in Panama 
weather conditions and therefore signal trans¬ 
mission are more uniform. Thus, in the rainy 
season, the temperature almost always lies be¬ 
tween 70 F and 85 F, and the relative humidity 
between 70 per cent and 100 per cent. The abso¬ 
lute humidity remains essentially constant. 


Only rarely does the wind velocity exceed 7 
mph. 

10. In practical outdoor situations, particu¬ 
larly in the jungles, signaling around obstacles 
is frequently less difficult than might be antici¬ 
pated from simple diffraction theory. 

11. Ambient noise was not a serious problem 
for ultrasonic signaling either in Pennsylvania 
or Panama. 



Chapter 8 

JUNGLE ACOUSTICS 

By Carl F. Eyring 


81 INTRODUCTION 

T his report is a summary of the work un¬ 
dertaken by Rutgers University under Con¬ 
tract OEMsr-1335 with OSRD. A nine-man ex¬ 
pedition conducted the field work in the Canal 
Zone as Project SC-105 under the general su¬ 
pervision of the Signal Officer, Panama Canal 
Department. Throughout the course of the in¬ 
vestigations close cooperation was maintained 
among the project personnel, the Army, and a 
similar expedition from Penn State College. 

The present project was undertaken for the 
purpose of investigating the types, magnitudes, 
and variations of noises which are indigenous 
to different kinds of jungle terrain under dif¬ 
ferent conditions of temperature, humidity, and 
wind velocity. The problems encountered on this 
project were somewhat similar to those arising 
in the project on ultrasonic signaling (see 
Chapter 7) except that in this case, the investi¬ 
gation concerned itself mainly with the detec¬ 
tion of audible aerial vibrations. 

Within a jungle, even more than in open ter¬ 
rain, information gained through hearing may 
be more important than that gained through 
sight. Two practical questions arise: (1) how 
quiet must a person be in order not to be de¬ 
tected by the enemy, who is known to be at a 
given location, and (2) how far away and in 
what direction is the enemy when certain recog¬ 
nized sounds are heard with a given loudness? 

A sound will be heard if it is loud enough at 
the source so that, after it has traveled over the 
terrain in question, it still has strength enough 
to compete successfully with the other sounds 
surrounding the listener. Obviously this is an 
oversimplified statement of the situation, but 
the statement does bring out the need of know¬ 
ing: 

1. The sound spectrograms of Army equip¬ 
ment, such as guns and vehicles; 

2. The sound transmission loss for the audi¬ 
ble frequencies over various types of terrain; 


3. The sound spectrograms of characteristic 
ambient noise. 

Problem 1, the sound spectrograms of certain 
Army equipment, machine guns, 1 and Army 
vehicles, 2 has already been solved. Problems 2 
and 3 were investigated under this project and 
the results obtained, together with the applica¬ 
tion of jungle acoustics to tactical problems and 
a consideration of micrometeorology in the 
tropics, form the substance of this report. 

Area of Operation. All measurements were 
made within 50 miles of headquarters, Fort 
Clayton, Canal Zone. Except for a few areas, 
all investigations were made in terrain north¬ 
ward of Summit and, therefore, on the Atlantic 
slope. 3 

Three li/o-ton trucks, a command car, and a 
jeep, furnished with drivers by the 10th Signal 
Company, served to transport equipment and 
personnel. 

The Jungle. Most jungle areas 4 investigated 
were in the Atlantic zone where “the high pre¬ 
cipitation produces a luxuriance of vegetation 
never equaled on the Pacific slope.” For over 
400 years Panama has been dominated by 
Europeans, and comparatively little virgin 
vegetation remains, this being true especially of 
the areas accessible by roads. Yet in spite of 
these facts certain areas, such as those chosen 
for study, have had time to take on an approx¬ 
imate virgin forest aspect and are as typi¬ 
cal of such a forest as the terrain on Barro 
Colorado Island, the “Canal Zone Biological 
Area.” 


82 TRANSMISSION LOSS 

MEASUREMENTS 

821 Apparatus and Method 

Sound Apparatus. Sounds of octave band 
width, essentially “filtered noise” resulting 
from passing through a filter set the amplified 


92 


ONFIDENTIAL \ 




TRANSMISSION LOSS MEASUREMENTS 


93 


output of a bank of direct-current-carrying car¬ 
bon resistors, were produced by loudspeakers 
placed at convenient positions in a more or less 
flat terrain. Microphones—no fewer than two, 
often as many as four—were located usually 
100 ft or more apart, on a straight line, the 
axis of the speakers. By the use of an electric 
circuit terminating in a power level recorder, 
the intensity levels of the sound at each micro¬ 
phone were recorded in turn. A comparison of 
these levels gave the drop in sound intensity 
level between microphone stations. 33 

Meteorological Equipment. Outdoor acoustics 
must always include the meteorology of the ter¬ 
rain. Continuous records, one of temperature 
and another of wind velocity, were obtained by 



Figure 1. Meteorological equipment in field. 


placing thermistors 315 in one arm of properly 
designed and calibrated bridges and recording 
(Figure 9) on Esterline-Angus meters the un¬ 
balance introduced when the thermistors 
changed in resistance, in one case, because of 
an atmospheric temperature shift when oper¬ 
ated cold (thermometer) and, in the other case, 
because of a wind velocity fluctuation when op¬ 
erated hot (anemometer). Relative humidity 
was measured by the use of a recording hair 
hygrometer which was always checked against 
a sling psychrometer. 

With few exceptions, readings were made at 
2 and 6 in., at 2, 5, and 10 ft, and at other se¬ 
lected elevations determined by the conditions 
at hand. The same heights were used for tem¬ 


perature as for wind velocity measurements; 
for the trip up as for the trip down. The differ¬ 
ent elevations were reached by attaching a pul¬ 
ley to lance poles, to a limb of a tree in the 
jungle, or to captive balloons, and passing over 
this pulley a cord which was attached to the 
thermistor housing (Figure 1). 

Care of Apparatus in Tropics. Because of 
moisture and fungi, it is difficult to keep elec¬ 
trical equipment in good working condition in 
the tropics. Great care was taken to store all the 
smaller pieces of equipment in drying cabinets, 
and to keep an electric light burning within the 
larger equipment, such as loudspeakers, when 
not in use. Not a single failure came because of 
the action of fungi, and moisture, the result of 
rain and dew, played only a delaying action. 


822 Definitions 

Transmission Loss (L). Transmission loss, 
measured in decibels, means the drop in sound 
intensity level, for whatever cause, as sound 
travels from one designated location to an¬ 
other, the nearer distance from the sound 
source being X lf the farther, X 2 . 

Terrain Loss (A). Terrain loss, measured in 
decibels, between any two specified distances 
from the sound source is the transmission loss 
between these points less that caused by the 
geometrical divergence of the sound beam. It 
is, therefore, a quantity which, when meas¬ 
ured over unit distances, can be attached to a 
given terrain, that is, a quantity which is de¬ 
termined by the nature of the ground covering, 
including the condition of the ambient atmos¬ 
phere. 

Terrain Loss Coefficient (a). The terrain loss 
coefficient, measured in decibels per foot, is de¬ 
fined by the relation: 

A A 

a = AX’ 

where A A is the terrain loss through a very 
short distance AX. Thus a is surely a function 
of the terrain (including kind of covering and 
condition of atmosphere), but it was not found 
to be a function of the distance, X, from the 


Confidential 






94 


JUNGLE ACOUSTICS 


sound source. Thus, since A increases linearly 
with distance between X x and X 2 , 

A 

01 ~ X 2 - Xf 

and the transmission loss between X x and X 2 
may be written as 

L = 20 log f- 2 + a{X 2 - X\). 

Al 

Profiles. A temperature profile is a plot of 
temperature in degrees Fahrenheit with height 


dient appeared in the atmosphere over the 
black, oiled runway. Toward evening this nega¬ 
tive gradient tended to decrease, and by early 
evening to disappear altogether. Preliminary 
tests and subsequent measurements and calcu¬ 
lations revealed an upward refraction of sound 
under the negative temperature gradient of 
midday, but no such refraction in early evening. 
At midday the shadow zone caused by refrac¬ 
tion, depicted in Figure 2 and calculated 30 on 
the assumption of no diffraction and scattering, 




above the ground in feet; a wind velocity pro¬ 
file is a similar plot of wind velocity in miles 
per hour and height in feet (see Figure 3). 

Temperature Gradient (S t ). The temperature 
gradient, in degrees Fahrenheit per foot, is the 
slope of the temperature profile curve. If the 
slope is negative, the gradient is known as a 
lapse rate; if positive, as an inversion. 

Wind Velocity Gradient (SJ. The wind ve¬ 
locity gradient, in miles per hour per foot, is 
the slope of the wind velocity profile. 

Measurements 

Hard Flat Surface. Under the heating of the 
tropical sun a steep negative temperature gra- 


was actually discovered for frequencies above 
2,000 c. For lower frequencies, and especially 
for those below 500 c, the shadow zone was defi¬ 
nitely blurred. It was found possible to elevate 
the microphone until it moved through the 
shadow and into the beam above (dotted line of 
October 30). With the effect of the upward re¬ 
fraction thus substantially reduced, the terrain 
loss might be expected to represent simply the 
loss caused by the moisture in an atmosphere 
with a relative humidity of 55 per cent and a 
temperature of 80 F. At the higher frequencies, 
the terrain loss coefficients agree remarkably 
well with Knudsen’s values 5 ’ 0 which he obtained 
indoors. 

With no temperature and wind gradients, re- 
























TRANSMISSION LOSS MEASUREMENTS 


95 


fraction would disappear, the shadow zone 
would be eliminated, and the microphones 
would not need to be elevated as before. Under 
this ideal condition (see Figure 3), no terrain 
loss was clearly shown for frequencies below 
500 c; however, the 7,000 and 10,000 c did show 
a set of experimental values which indicate a 


ments having been made under very small tem¬ 
perature and wind velocity gradients. 

A study of the curves of Figure 4, labeled to 
agree with the situations just described, re¬ 
veals (1) that a rapid rise takes place in the 
terrain loss coefficient beginning first at about 
300 c, and then again at about 4,000 c; (2) that 


Table 1 



75 

150 

300 

600 

1,200 

2,400 



Frequency, c 

150 

300 

600 

1,200 

2,400 

4,800 

7,000 

10,000 

a db per ft (our value) 

0 

0 

0.01 

0 

0.015 

0.011 

0.020 

0.045 

P db per ft (Knudsen’s) 

0 

0 

0 

0.001 

0.002 

0.006 

0.019 

0.033 


linear relationship between terrain loss and 
range and, therefore, a constant terrain loss co¬ 
efficient, presumably a loss caused by moisture 
in an atmosphere with a relative humidity of 95 
per cent and a temperature of 76 F. As before, 
a comparison is made with Knudsen’s values. 


Table 2 


Frequency,c 

7,000 

10,000 

a db per ft (our value) 

0.015 

0.027 

P db per ft (Knudsen’s) 

0.0145 

0.0265 


In summary the following conclusions may be 
drawn. Over open terrain during daytime, nega¬ 
tive temperature gradients are very large (Fig¬ 
ure 2) and the upward refraction produced, 
especially for the higher frequencies, greatly in¬ 
creases the terrain loss near the earth’s surface. 
At night (Figure 3), if the sky is overcast, the 
upward refraction becomes much less, and the 
terrain loss approximates that due to atmos¬ 
pheric moisture; if the sky is clear, downward 
refraction and a further decrease in terrain loss 
appear an hour or more after sunset. (See 
Table 3 for estimated terrain loss coefficients 
for a large variety of meteorological condi¬ 
tions.) 

Grass Areas. Five situations were chosen 3 ' 1 : 

(A) over thinly covered short (6-12 in.) grass; 

(B) over thickly covered short (18 in.) grass; 

(C) through thickly covered short grass; (D) 
through shrubbery and over thick short grass; 
(E) through thick tall (6 ft) grass. The meas¬ 
ured terrain loss coefficients are depicted in Fig¬ 
ure 4 and are free, as nearly as practicable, 
from the effects of refraction, the measure- 


between about 600 c and 3,000 c the coefficient 
for a given terrain remains substantially con¬ 
stant; (3) that for frequencies up to 400 c the 


TEMPERATURE PROFILE 


* 






17133 

BROKEN 1 

is: 13 

BROKEN 


19:10 
SC CL 


21120 

BROKEN 


23:20 

BROKEN 










- H VS T 

-H VS AT 




’t 














M 








1 



1 

1 



L i 

> A. 

74 

( 

N ■ 

7 

L. 

i 7 

7 

\ , 
5 


7 

r 

\ 

4 

i 

» 7 

1, 

3 



TEMPERATURE — F 

O 2 O 20 20 2 O 2 4 

AT - F 


WIND PROFILE 





J 

i 1 


17:33 

E 


1 

19:18 

E 


j 

23*.20 

N W 

l 





ft 

1 ' 

-H VS V 

-H VS AV 

1 



,jl 




/ 

/ \ 



1 

1 



/ 




1 ] 



1 

\ 



V 

0 


\ c 

V 

> 

2 * 

\ 

~7 

t 

r- 

6 


VELOCITY AND CHANGE IN VELOCITY IN MILES PER HOUR 


Figure 3. Temperature and wind profiles, Mad¬ 
den Field Runway, night, November 13, 1944. 

coefficients for tall and for short grass and for 
shrubbery-covered short grass are approxi¬ 
mately of the same magnitude; (4) that for 
frequencies above 500 c the coefficient is very 






















































96 


JUNGLE ACOUSTICS 


sensitive to the type of terrain, for frequencies 
below 300 c very insensitive. No theory is ad¬ 
vanced to explain these observations. 

The Tropical Forest. It was found possible 
to type the tropical jungle as follows: (1) very 
leafy, one sees a distance of approximately 20 
ft, penetrated by cutting; (2) very leafy, one 
sees a distance of approximately 50 ft, pene¬ 
trated with difficulty but without cutting; (3) 



areas. 

leafy, one sees a distance of approximately 100 
ft, free walking if care is taken; (4) leafy, one 
sees a distance of approximately 200 ft, pene¬ 
tration is rather easy; (5) little leafy under¬ 
growth, large bracketed trunks, one sees a dis¬ 
tance of approximately 300 ft, penetration is 
easy. By careful selection, representatives of all 
five types were found and studied. 

Within the jungle the temperature and wind 
velocity gradients were found to be so small 
that the sound refraction which they produce 
could be neglected for all practical purposes. 
The terrain loss coefficients, found to be inde¬ 


pendent of range, for the various types of 
jungle are summarized in Figure 5, zones being 
designated to represent the five jungle types de¬ 
scribed above. 


« 3 AMBIENT SOUND OF THE JUNGLE 

Jungle Sounds. A jungle far removed from 
human activities at times may be deathly silent. 
At other times it is filled with animal sounds: 
humming, buzzing, chirping, noisy and musical 
“mate” calls; with the rustle of palms under 
wind action; with the sound of dropping and 
rushing water, the result of heavy dew and 
rain; and even with the sound of thunder. Sel¬ 
dom, if ever, do all possible jungle sounds join 
in a grand finale. When rain and wind are at 
their height, animal life is usually quiet; when 
the weather is fine, birds sing at daybreak; but 
insects, which have maintained a chorus all 
night, slowly bring their night calling to a close. 

The songs of birds and the calls of insects and 
amphibia are primarily indications of the 
breeding season, and, since this period is of 
comparatively short duration and for each in¬ 
dividual occurs only once a year, the major 
sounds produced by them are distinctly cyclical. 
In the tropics, however, there is not the concen¬ 
tration of breeding seasons of many species into 
a few months that one finds in northern lati¬ 
tudes. While the peak of the breeding season 
for birds, for example, probably occurs in April, 
there are some birds nesting every month of the 
year, and the main period extends from Febru¬ 
ary to July. In the case of amphibia, the breed¬ 
ing seasons and resulting calls seem even less 
regular than with birds and are more dependent 
on water conditions. Even in one spot like 
Barro Colorado Island, all individuals of one 
species do not seem to come into breeding ac¬ 
tivity at the same time, as they do in northern 
latitudes, with the result that there will be 
feverish activity and much singing for a few 
days followed by a lapse of a week or more with 
no activity. This all helps to make the general 
picture of animate sound in the jungle rather 
complicated. 4 ® 

Recordings of Jungle Sounds. Except for the 
recording of mammal voices, such as those of 


ONFIDENTIAL j 























AMBIENT SOUND OF THE JUNGLE 


97 


the howling monkey with wide band sounds, the 
microphone was placed at the focus of a 40-in. 
parabola (see Figure 6) with a resulting gain 
of from 10 to 25 db and with no noticeable dis¬ 
tortion for bird, insect, and amphibian calls. 
Recordings were made on acetate-coated alumi¬ 
num disks by the use of Presto disk recording 
equipment. 


resent a series of recordings made with the 
microphone at a definite spot during a 24-hour 
period. There will likewise be found on the 
disks recordings of a few inanimate sounds such 
as wind, rain, thunder, and running water, as 
well as airplanes, locomotives, motorboats, etc. 4b 

Ambient Sound Levels. During early Decem¬ 
ber, two 24-hour records of ambient sound 



Figure 5. A chart from which to estimate terrain loss coefficients for tropical jungles (see text for de¬ 
scription of zones). 


Altogether, recordings have been made on 
57 double-faced records which will require 23 
hours of constant playing time. These record¬ 
ings represent 95 species, of which 78 are birds, 
4 are mammals, 9 are amphibia, and 4 are in¬ 
sects. In addition, of course, a small part of the 
recording is of the general background in dif¬ 
ferent spots where work was done. Some of 
these recordings represent just a minute or so 
at daybreak or shortly thereafter; others rep- 


levels were obtained: the first, during fair 
weather; the second, during stormy weather. 
The microphone was placed well within the 
jungle and approximately 300 ft from the meas¬ 
uring equipment. Readings of levels were made 
every 30 minutes for overall and for seven 
frequency bands. The equipment was standard¬ 
ized against a calibrated condenser microphone 
(Western Electric 640-AA, No. 428), and the 
field microphone was furnished with a heating 
















































































98 


JUNGLE ACOUSTICS 


coil to keep it free from heavy dew during the 
night. 

The intensity levels measured every 30 min¬ 
utes during the 24-hour runs were averaged for 
2-hour intervals, and out of these averages a 
set of masking curves was plotted. 3e Also day¬ 
time and night averages were obtained. The 
daytime average for a wet day in a typical 
jungle (Las Cruces Jungle) is plotted in Fig¬ 
ure 7 as jungle ambient noise. 

Judging Sound Direction in a Jungle. The 
method consisted of three steps: the random 
firing of guns at selected locations in the jungle 


4. Within the range studied—300 to 600 ft— 
the error decreases with the distance from the 
source. 

5. Hearing two shots fired in succession in the 
same general direction does not help in deter¬ 
mining the direction of the second shot. (This 
might not apply if, by the time the second shot 
is fired, the head had been turned to a more 
effective angle, see 9 below. Such a technique 
was not permitted in the experiment.) 

6. There is a tendency to fail to remember 
the exact orientation of the head at the time a 
sound is heard, and this may lead to recorded 



Figure 6. Parabolic reflector in use. 


—locations not known to the listeners—the 
judging of the sound direction for each shot, 
and the recording of each judgment on a spe¬ 
cially prepared chart. For details see the orig¬ 
inal report. 3 ' 

In judging the direction of a shot in a jungle, 
the following conclusions seem to be supported 
by field measurements: 

1. The probable error of judgment is large, 
of the order of 16.5 degrees. 

2. The error is greatest if the sound source 
is either directly in front or in back—the error 
may even show marked confusion in these di¬ 
rections. 

3. The error is least if the sound source is 
near the axis passing through the ears. 


judgments with persistent errors in one direc¬ 
tion—to the right, for example. 

7. There is a minor tendency to bring the 
observed direction into line with the axis pass¬ 
ing between the ears. 

8. Some observers are better than others— 
abilities seem to follow a normal distribution. 

9. Although the response of a jungle to the 
sound produced in it will continue to be a 
hindrance, there is reason to believe that sound 
direction judgments may be improved by fol¬ 
lowing two simple rules based on the facts 
brought out in this investigation: (a) keep the 
orientation of the head at the time when the 
sound was heard clearly in mind; (b) remem¬ 
ber that smaller errors are made when the sound 






JUNGLE ACOUSTICS APPLIED TO TACTICAL PROBLEMS 


99 


source is near the axis passing between the 
ears. 


84 JUNGLE ACOUSTICS APPLIED TO 
TACTICAL PROBLEMS 

The Problem. The application of jungle 
acoustics to tactical problems will be illustrated 
by solving a specific problem: how far away is 


few soldiers in most groups have hearing so 
acute that the solid threshold of hearing curve 
would best represent their hearing. They would 
be able to hear a 500-c tone, for example, when 
its intensity level reached 8 db, and would show 
a 15-db advantage over the average soldier— 
an advantage of no use on a noisy battlefield, 
but in a jungle of great value, as will be seen. 

Masking of Ambient Noise. The next step is 
to find the deafening effect of the natural 



a 21 / 2 -ton Army truck when it can just be heard 
through a tropical jungle? 

Obviously, not all 214-ton Army trucks make 
the same noise under all conditions, and tropical 
jungles differ in density, yet the average truck 
and the typical jungle may be used and the 
problem solved. The solution is made in steps. 

The Listener. The listener is assumed to be a 
young soldier with hearing at least as good as 
the best 50 per cent of a typical American 
group. If so, his threshold of hearing is repre¬ 
sented by the dashed line in Figure 7. This 
means that, wityi no other sounds present, a 
pure tone of a given frequency can just be 
heard by this soldier when its intensity level 
reaches the dashed line in the figure. A very 


sounds of a jungle. The ambient noise masking 
level curve for daytime on a wet day in a typical 
jungle is shown in Figure 7. Below 1,000 c the 
ambient noise masking level curve either is 
below or just touches the threshold of hearing 
curve of the average soldier listener. This 
means that for frequencies below 1,000 c the 
average soldier is not deafened by the noisy 
background found in a wet season jungle. This 
statement applies only to the quiet periods be¬ 
tween animal calls, because the peaks were not 
included in the noise measurements; only the 
general more or less steady background out of 
which the occasional calls appear was measured. 
The soldier will usually be able to select these 
quiet periods; therefore, the ambient noise 







































































100 


JUNGLE ACOUSTICS 


masking level curve submitted is the one to use 
in practical problems. 

It is important to observe that, between 
1,000 c and 400 c, the average soldier will hear 
as well as the one with very acute hearing, be¬ 
cause the latter will be deafened by the ambient 
noise just enough to render him average also. 
But below 400 c the one with acute hearing will 
have a definite advantage. This means that 
jungle listening should be assigned to those 
known to have better than average hearing in 
the range below 500 c. 

In the jungle the air is usually very still, but 
in open terrain the wind velocity in the tropics, 
though seldom high, may exceed 10 mph. A 
listener in such a wind, even though otherwise 
all is quiet, will be slightly deafened. This may 
be verified by referring to Figure 7 and observ¬ 
ing the masking level curve of a 6- to 13-mph 
wind. 7 The soldier with acute hearing has no 
advantage over the average soldier in such a 
wind. Notice that the masking at 200 c is 3 db— 
this information will be needed later. 

Sound from Truck. Recent studies 2 give the 
distribution-in-frequency of the sounds from 
various Army vehicles, as measured 100 ft 
away. The published curves are presented on 
the basis of octave bands; the one used for a 
21 / 2 -ton Army truck, and depicted in Figure 7, 
has been changed to the basis of critical band 
widths so that all curves in the figure might be 
comparable. 8 ’ 9 

Intensity Level Available for Transmission 
Loss. In the jungle the hearing of the average 
soldier is limited, as has been shown, by his 
threshold of hearing up to 1,000 c and by the 
masking of jungle noise for frequencies above 
that. The difference in level between the mask¬ 
ing level curve of the truck noise at 100 ft from 
the source and the soldier’s modified threshold 
curve is at a maximum between 200 and 500 c. 

As the sound from the truck passes through 
the jungle, it suffers transmission loss, and 
therefore the masking level curve represent¬ 
ing the decreasing truck noise will move 
steadily down in level. But, since the terrain 
loss coefficient goes up with increasing fre¬ 
quency, the curve will also get steeper and 
steeper as it moves downward in level. Were it 
not for this rotation, one would expect to hear 


the truck last in the frequency band between 
200 and 500 c, the band with maximum ordi¬ 
nates as explained above. But the rotation, 
resulting from the increase in terrain loss with 
frequency, permits the 200 c to be heard last, 
and it becomes the so-called optimum frequency. 
The difference in level between the two curves 
at 200 c is 32 db, and this represents the level 
available for transmission loss. (The soldier 
with acute hearing would have 40 db available. 
In a wind of 6 to 13 mph they both would have 
29 db available.) 

Distance of Truck from Listener. From the 
discussion so far it is clear that, if the truck is 
just to be heard, 32 db are available for trans¬ 
mission loss. To what distance in the jungle 
does this loss correspond? 

First, the terrain loss coefficient must be de¬ 
termined. The jungle which will be considered 
typical lies at the center of Zone 3, Figure 5. 
The jungle represented by this zone is leafy, 
free walking is possible if judgment is used in 
selecting the path, and with care a person may 
see a distance of 100 ft. The chart, Figure 5, 
indicates that 0.02 db per ft would properly 
represent this jungle for the frequency of 200 c. 

With the terrain loss coefficient and the level 
available for loss determined, the next step is 
to find the distance by using the set of curves 
shown in Figure 8. Select the curve correspond¬ 
ing to a coefficient of 0.02; follow out on this 
line until it has climbed 32 db, and read the 
distance 750 ft. This is the answer. If an “aver¬ 
age” 2 !/ 2 -ton truck is just heard by an “average” 
soldier in a “typical” jungle on a day in the 
wet season, it probably is 750 ft away. If just 
heard by a soldier with acute hearing (40 db 
available) or if the average soldier recognizes 
the truck by its peaks of noise, thus gaining 
from 8 to 10 db, it is probably 1,000 ft away. 
An experiment was set up to check this solution. 
The agreement between calculation and experi¬ 
ment was satisfactory. 3 ^ 

Summary of Data. As a summary it seems 
wise to put down in tabular form the terrain 
loss coefficients which seem to be appropriate 
to use for several kinds of terrain under various 
weather conditions, and also tfie intensity level 
available for transmission loss when listening 
for Army vehicles. It will be assumed that the 






JUNGLE ACOUSTICS APPLIED TO TACTICAL PROBLEMS 


101 


listener is in the tropics, that the sound source Terrain loss coefficients for open terrain are 
and ear are 5 ft above the ground, that the so dependent on weather that the values listed 
optimum frequency at which the sound will be in Table 3 must be thought of as estimates; yet 

TERRAIN LOSS COEFFICIENT-DB PER FT 



Figure 8. Transmission loss as a function of distance. 


heard is 200 c (the frequency which seems the values do have a foundation in field meas- 
optimum in a jungle for all Army vehicles), urements in the tropics and in the temperate 
that the only local noise is that natural to a zone. 7 Because of a change of vegetation with 

Table 3. Estimated terrain loss coefficients for open terrain—200 c. 

a (db per ft) 


Weather 

Bare or thin grass 

Thick grass 

Midday, sky clear 

Wind under 6 mph or cross wind 

0.005-0.01 

0.008-0.01 

Head wind 6-12 mph 

0.008-0.012 

0.008-0.012 

Tail wind 6-12 mph 

0.005 

0.005 

Midday, overcast, or early morning or evening, clear 

Wind under 6 mph or cross wind 

0.003 

0.006 

Head wind 6-12 mph 

0.006 

0.010 

Tail wind 6-12 mph 

0.002 

0.005 

Night, sky overcast 

Wind under 6 mph or cross wind 

0.002 

0.005 

Head wind 6-12 mph 

0.005 

0.009 

Tail wind 6-12 mph 

0.001 

0.004 

Night, sky clear 

Wind under 6 mph or cross wind 

0.001 

0.004 

Head wind 6-12 mph 

0.005 

0.008 

Tail wind 6-12 mph 

0.000 

0.003 


quiet terrain and that for the average ear there the season, a jungle should be typed every time 
is no masking if the wind is below 6 mph, and it is involved in a sound transmission problem. 
3 db masking if the wind reaches 13 mph. At the optimum frequency for listening to Army 














































102 


JUNGLE ACOUSTICS 


vehicles, 200 c, the terrain loss coefficient in 
the jungle is essentially independent of daily 
weather changes. 


Table 4. Terrain loss coefficients for jungles— 
200 c. 


Type of jungle (see text) 

a (db per ft) 

1 

0.04 

2 

0.03 

3 

0.02 

4 

0.015 


MICROMETEOROLOGY IN THE 
TROPICS 


Apparatus and Definitions 

Thermistors, used as thermometers and ane¬ 
mometers, were found to be rugged in construc¬ 
tion, accurate and reliable in operation, respon¬ 
sive to rapid changes in temperature and wind 
velocity, and light in weight. Hydrogen-filled 


Table 5. Intensity level available for transmission 
loss. 


Vehicle 

Wind velocity 

Kind 

Speed (mph) 

0-6 mph 

6-13 mph 

Jeep 

15 

19 

16 

%-ton truck 

15 

23 

20 

2%-ton truck 

12 

32 

29 

M5 tractor 

10 

43 

40 

8-ton truck 

11 

48 

45 


balloons were found useful, both in and out of 
the jungle, to gain measurements to moderate 
heights (150 ft maximum). Meteorological field 
measurements were made over hard smooth 
surfaces, over short grass, in and over tall 
grass, in and over low shrubbery, in and over 
tropical forests. In all these situations 311 tem¬ 
perature and wind velocity gradients (illus¬ 
trated in Figures 2 and 3) were obtained, and 
from the continuous records, Figure 9, temper¬ 
ature and wind velocity fluctuations and vari¬ 
abilities were determined in keeping with the 
following definitions: 

Temperature and Wind Velocity Fluctuation. 
The number of times a temperature or wind 
velocity record (see Figure 9) has a zero slope 
during a half-minute interval is called the 
fluctuation of the temperature or the wind ve¬ 


locity. This number, designated as the number 
of vacillations per half-minute, includes all 
maxima, minima, and points of inflection with 
zero slope. Unless the recording equipment has 
a zero time constant, the fluctuation will be a 
function of the equipment as well as of the 
micrometeorological elements. Yet for a given 
equipment, a comparison of these numbers, ob- 




Figuee 9. Temperature and wind velocity rec¬ 
ords, Madden Field Runway, October 26, 1944, 
1227 EST. 

tained for different meteorological situations, 
may be made with profit. 

Temperature Variability (A T). One-half of 
the difference between the maximum and mini¬ 
mum temperature recorded within a half-min¬ 
ute interval is called the temperature variability 
for the specified position and time of day. 

Wind Velocity Variability (AU). One-half of 
the difference between the maximum and mini- 


CONFIDENTIAL \ 









































































































MICROMETEOROLOGY IN THE TROPICS 


103 


mum wind velocities recorded within a half- 8S - 2 Summary of Temperature Data 
minute interval is called the wind velocity vari¬ 
ability for the specified position and time of day. Spread of Diurnal Temperature. The spread 
Gustiness (G). The ratio, expressed in per of diurnal temperature is a function of the 




Figure 10. (A) Temperature gradients above and below canopy, Las Cruces Jungle, December 4 and 5, 

1944. (B) Temperature gradients, Las Cruces Jungle, November 23, 1944, and Clayton Golf Course, 
December 6, 1944. 

cent, of twice the wind variability to the aver- density of cover, the conditions of the sky, the 
age wind velocity is called the per cent of gusti- circulation of the air, and the altitude of the ter- 
ness. rain. Over grass or above the canopy of a forest, 











104 


JUNGLE ACOUSTICS 


the temperature spread in Panama is approxi¬ 
mately from 66 F to 86 F. 

Temperature Gradient. In Figure 10, diurnal 
temperature gradients are shown (A) for posi¬ 
tions above and below a jungle canopy, and 
(B) for positions under the canopy of a jungle 
and over a grass area. Average temperature 
gradients, thought to be characteristic of Pan¬ 
ama terrain and based on a 5-ft layer of atmos¬ 
phere just above the terrain described, are sum- 


8 3 3 Summary of Wind Velocity 
Measurements 

Wind Velocity. Measured wind velocities are 
summarized in Table 7. 

Wind Velocity Gradients. Under the jungle 
canopy the wind velocity gradient is substan¬ 
tially zero; over the canopy or in open terrain 
it may reach 0.5 mph per ft. 

Wind Velocity Fluctuation. Above the jungle 


Table 6 


Average 

value 


Time 

Terrain 

Kind of 
gradient 

(degrees F 
per ft) 

Description of value 

Day 

Bare 

Lapse rate 

—2.0 

Maximum 

Day 

Grassy 

Lapse rate 

—1.5 

Maximum 

0900-1500 

Forest canopy 

Lapse rate 

—0.1 

Maximum 

0700-1800 

Under canopy at ground 

Inversion 

+0.5 

Maximum 

0700-1800 

Under canopy at ground 

Inversion 

+0.2 

Common 

0700 

Earth’s surface 

Isothermal 

0.0 

Less than one hour’s duration 

Night 

Bare 

Inversion 

+1.2 

Maximum 

Night 

Grassy 

Inversion 

+1.0 

Maximum 

1500-0900 

Forest canopy 

Inversion 

+0.1 

Maximum 

1800-0900 

Under canopy at ground 

Lapse rate 

—0.2 

Maximum 

1800-0900 

Under canopy at ground 

Lapse rate 

—0.1 

Common 

1700 

Earth’s surface 

Isothermal 

0.0 

Less than one hour’s duration 


marized in Table 6. The time designated may 
be in error as much as one hour, because of the 
variability of sky cover, wind, etc. 

Temperature Fluctuation. Temperature fluc¬ 
tuations reach a high of about 20 vacillations 
per half-minute over a bare heated surface and 
a low of about 3 vacillations per half-minute in 
the deep jungle. 

Temperature Variability. Temperature vari¬ 
ability, which is a function of the kind of sur¬ 
face heated, the intensity of the sunlight, the 
circulation of the air and other factors, is great¬ 
est during daytime and least at night. Over 
bare terrain and near the surface, it may reach 
4 F during daytime and drop to 0.5 F at night. 
Over a grass area its maximum is 2 F. Under a 
forest canopy it seldom reaches 0.5 F but often 
falls to 0.1 F. In general the variability de¬ 
creases ivith increased elevation, changing over 
bare terrain from 4 F at the surface to 2 F at 
an elevation of 10 ft, for example. 


Table 7 

Maximum velocity recorded 17 mph 

Under the jungle canopy a maximum of 2 mph 

Under the jungle canopy usually less than 1 mph 

Over the canopy and open areas 1 to 17 mph 


canopy and in open terrain the wind velocity 
fluctuations approximate 15 vacillations per 
half-minute, and this value is substantially in¬ 
dependent of time of day and elevation. In a 
jungle the vacillations per half-minute are very 
few in number. 

Wind Velocity Variability. The wind velocity 
variability generally increases ivith altitude and 
is very often equal to half the average wind 
velocity. 

Gustiness. Gustiness is high both under and 
over the jungle canopy and over open terrain, 
often reaching 100 per cent, sometimes 200 per 
cent. 









MICROMETEOROLOGY IN THE TROPICS 


105 


Humidity Measurements 

Humidity. Relative humidity in a jungle is 
always high; it is near 100 per cent about 
eighteen hours out of the twenty-four; the pe¬ 
riod of reduced humidity, when during midday 
relative humidity may fall for a short time to 
60 per cent, is often as long as six hours for a 


dry season type of day, but may shorten to 
a few hours for a wet season type of day. At 
night in the jungle relative humidity is inde¬ 
pendent of elevation, but during the day it is 
greatest near the ground. An open terrain shows 
about eight hours per day of high humidity. 
During the period of reduced humidity, rela¬ 
tive humidity seldom drops below 50 per cent. 




Chapter 9 

ATTENUATION OF SOUND IN THE ATMOSPHERE 

By V. O. Knudsen 


91 INTRODUCTION 

B efore the effect of a given sound can be 
evaluated, and before various desired 
sounds can be successfully produced, it is first 
desirable to investigate the factors which cause 
energy losses in sound waves of finite amplitude 
when propagated through the atmosphere. 1 ’ 2 
Consequently, this investigation was under¬ 
taken, as a part of the project on sound sources, 
to evaluate the various factors responsible for 
energy losses in the transmission of intense 
sounds in air, especially for the frequency range 
of 500 to 1,000 c. These factors are: (1) ab¬ 
sorption at large amplitudes owing to the non¬ 
linearity of the medium; (2) absorption from 
molecular collisions, viscosity, and heat conduc¬ 
tion; (3) losses from scattering owing to turbu¬ 
lence in the atmosphere; and (4) influence of 
the terrain over which the sound is propagated. 


92 ABSORPTION OF SOUND WAVES OF 
FINITE AMPLITUDES 

1. Point source measurements. Using the 
Western Electric 598-B loudspeaker unit a (horn 
removed) in a 4-ft baffle as a point source of 
sound at 500, 1,000, or 2,000 c in the open air 
and also in a room with boundaries so absorp¬ 
tive that reflections from the boundaries can be 
neglected, it was found that the sound pressure 
varied as 1/r, where r is the distance from the 
source, for values of r from about 10 cm to 
100 cm and for intensity levels of less than 
140 db (the highest level obtainable). Thus, at 
these frequencies, intensity levels, and short 
ranges, there were no appreciable losses. 

2. Two-microphone measurements. In the 
point source measurements just described there 


a This unit, from which the folded, exponential horn 
was removed for this part of the investigation, has an 
8-in. diaphragm and is capable of delivering (with horn 
attached) 500 watts of acoustical power at 500 to 1,000 c. 


was considerable uncertainty in measuring the 
distance r between source and microphone. In 
order to avoid this uncertainty, two micro¬ 
phones were located at fixed distances r x and r 2 , 
and the difference in intensity level at the two 
microphones was observed as the intensity of 
the source was increased. If this difference re¬ 
mains constant as the intensity of the source is 
increased, it can be concluded that there are 
no losses between r x and r 2 which depend upon 
the intensity. In these experiments, this differ¬ 
ence did remain constant for frequencies of 500 
to 4,000 c at intensity levels up to 144 db, again 
indicating no appreciable nonlinear losses. 

3. Absorption in tubes. Preliminary experi¬ 
ments using a 3-in. tube driven by the 598-B 
unit indicated that there were no measurable 
nonlinear losses for intensity levels up to 144 db. 
After modifying the driver and tube so as to 
give higher intensity levels, measurable losses 
of about 0.5 db per m began at 160 db and 
increased to about 1.5 db per m at 165 db, the 
highest level at which data were obtained in 
this investigation. These losses are about twice 
as large as those predicted by extant theory on 
waves of finite amplitude. 

From the foregoing experiments it is con¬ 
cluded that for intensity levels up to 155 db the 
nonlinear losses were too small to be measured 
and that the total losses cannot be much greater 
than those resulting from molecular collisions, 
viscosity, and heat conduction. However, non¬ 
linear losses became appreciable at levels of 
160 db, and at 165 db have increased to about 
1.5 db per m. Undoubtedly, the rate of loss will 
continue to increase as the level rises above 
165 db. 

93 ATTENUATION OF SOUND WAVES 

OF SMALL AMPLITUDES—ABSORPTION 
AND SCATTERING 

The experiments described in Section 9.2 in¬ 
dicate that at intensity levels below about 150 




ATTENUATION OF SOUND WAVES OF SMALL AMPLITUDES 


107 


db the nonlinear losses are negligible. It is to 
be expected therefore that at such levels the 
losses will be (1) absorption resulting from 
molecular collisions, viscosity, and heat conduc¬ 
tion, and (2) scattering from inhomogeneities 
in the atmosphere. The absorbed sound can be 
calculated; at the frequencies of interest to this 
project, that resulting from molecular collisions 
is predominant, and the remainder can be neg¬ 
lected. If the measured losses agree with this 
calculated absorption, it can be concluded that 



all other losses, including scattering, are neg¬ 
ligible. 

This conclusion is indeed supported by the 
following experiments. 

1. Integration measurements. The sound 
power radiated from a point source within a 
given solid angle would be conserved as it is 
propagated away from the source if there is no 
absorption or scattering. Conversely, if the 
power flux within the same solid angle is less 
at a distance r 2 than it is at a distance r x 
(r 2 > r x ), then there are losses from absorption 
and/or scattering. Suppose P x is the power flux 
at r x and P, that at r 2 . Then the transmission 
loss [TL] in decibels per unit length is 


TL = 


10 , Pi 

r 2 - n log PS 


( 1 ) 


Measurements of this TL were made in the 
open air, using as a source the 598-B speaker 
mounted on an inclined track in a large rectan¬ 
gular body on a 11/2 -ton truck. The speaker can 
be pulled to the top of the truck’s body and 
projected vertically through a hole in the roof 
(the roof serving as a baffle), or lowered to 
the bottom of the track and projected hori¬ 
zontally through a baffle board attached to the 
rear of the truck’s body. Most of the tests were 
made with the sound projected vertically up¬ 
ward. The general arrangement is shown in 
Figure 1. P x and P 2 were determined by means 
of a sound level recorder associated with two 
microphones. M x and M 2 were kept at distances 
r x and r 2 from the source by means of a balloon 
and guy wires. These could be moved slowly, 
along arcs of radii r x and r 2 , across the center 
of the solid angle (which is symmetrically dis¬ 
posed around the axis of sound beam) in which 
the sound power flux was measured. The power 
flux through a given zone is then proportional 
to product of the average squared pressure 
over the zone times the area of the zone. When 
these quantities are summed for the entire solid 
angle considered (usually the one-half plane 
angle was 5 degrees) at r x and r 2 , the two re¬ 
sulting numbers are proportional to P x and P 2 , 
and the ratio of the two numbers is PJP 2 . The 
TL can then be calculated by equation (1). In 
a series of 37 sets of measurements for a tone 
of 500 c and for distances up to 90 m, the ob¬ 
served attenuation ranged from —0.0400 to 
0.0600 db per m, with a mean value of 0.0125 
± 0.0013 db per m. 

2. Two-microphone measurements. In a series 
of measurements similar to those described in 
Section 9.2, but for vertical projection, the at¬ 
tenuation in desert air (about 25 C and 20 to 25 
per cent relative humidity) was too small at 
500 and 1,000 c to be measured by this method, 
but at 2,000 c the observed attenuation was 
0.06 db per m and at 4,000 c it was 0.09 db 
per m. This result for 4,000 c compares with 
about 0.06 db per m which is estimated for air 
of about the same temperature and humidity 
from more reliable measurements made in re¬ 
verberation chambers. 3 

All the experiments conducted on the atten¬ 
uation of sound in the open air during this in- 


CONFIDENTIAL : 












108 


ATTENUATION OF SOUND IN THE ATMOSPHERE 


vestigation support the conclusion that losses 
from scattering are not large—probably less 
than 0.01 db per m for usual atmospheric con¬ 
ditions—and that at frequencies of about 2,000 
to 4,000 c the principal loss can be accounted 
for by molecular absorption. 



Figure 2. Propagation over a reflecting surface. 


where k = 2tt/a, p t) is the maximum instantane¬ 
ous sound pressure at P from the direct sound 
wave alone, and x is the phase angle introduced 
at the ground reflection. 

If the specific acoustic impedance of the 
ground is greater than that for air, the angle x 
will be zero, and equation (2) becomes 


P 


tp 0 

= -^r cos 


kAY 

x • 


(3) 


If the ground is a porous absorber, in which 
the specific acoustic impedance is less than that 
for air, the angle x will approach x and equa¬ 
tion (2) then becomes 


P = 



kAY 
X ' 


(4) 


9 4 TRANSMISSION OF SOUND OVER 
DIFFERENT TYPES OF TERRAIN 


It will be seen from equations (3) and (4) that 
when kAY/X is very small, the sound pressure 


In the practical case of the transmission of 
sound over the ground, the nature of the terrain 
may greatly influence the transmission. A typi¬ 
cal case is illustrated in Figure 2. The source S 
is located at a height A above a level terrain. 
The sound field at P is made up principally of 
two components, that which comes directly 
from S and that which has been reflected from 



DISTANCE IN METERS 

Figure 3. Intensity as a function of distance. 

the ground (and appears to come from the 
image of S, i.e., from S'). 

If A and Y are small compared to X, and the 
reflection coefficient is unity, the absolute value 
of the sound pressure at P is 

2p 0 / kA Y a \ 

P = ~x cos \~Y~ + 2 )’ (2) 



Figure 4. Intensity as a function of distance. 


at the point P varies inversely as the distance X 
when there is no change of phase at reflection, 
but varies inversely as the square of X when 
there is a phase change of 180 degrees. 

Measurements of the sound field made over 
different terrains revealed that the sound pres¬ 
sure was given either by equation (3) or equa¬ 
tion (4). The results for two different ter¬ 
rains are shown in Figures 3 and 4, for 
A = Y = 1.5 m. Figure 3 is for a mowed grass 
field for which it appears the grazing incidence 
sound was reflected with a change of phase of 
180 degrees, and Figure 4 is for a hard dirt 
field for which it appears there was no phase 
change at reflection. 

























































OTHER FACTORS AFFECTING TRANSMISSION LOSS 


109 


Measurements made over other terrains in¬ 
dicated that, at least approximately, a dry lake 
surface (many cracks penetrating surface), an 
alfalfa field, brush 18 in. high, brush 3 ft high 
(in clumps), and brush 3 ft to 5 ft high, all 
introduced a phase change of 180 degrees at 
reflection, that is, the distribution of sound 
pressure conformed well with equation (4) ; 
whereas the sound field over an asphalt road as 
well as the hard dirt field conformed with 
equation (3). 

As a further check of the applicability of 
equations (3) and (4), measurements were made 



HEIGHT IN METERS 

Figure 5. Intensity as a function of height. 

of the vertical distribution of the sound inten¬ 
sity level at various distances from the source. 
Figures 5 and 6 show the results obtained over 
an asphalt street and a mowed grass field, re¬ 
spectively. 

Inasmuch as most surfaces likely to be en¬ 
countered in warfare are probably of the type 
which will introduce a phase change of about 
180 degrees for reflection of sound at near 
grazing incidence, the interference between the 
direct and reflected rays of sound appears to 
be the controlling factor in determining the 
transmission loss. For the frequencies here con¬ 
sidered, this loss is far greater than the com¬ 
bined effects of absorption and scattering. 


95 OTHER FACTORS AFFECTING 
TRANSMISSION LOSS 

For long-range propagation of sound, tem¬ 
perature and wind refraction are often the con¬ 
trolling factors. However, since the present in¬ 
vestigation was limited to short-range propa¬ 
gation of sound, these factors were generally 
negligible. It was necessary, however, to make 
the foregoing measurements only when the 
wind speed was less than about 400 ft per min. 



Figure 6. Intensity as a function of height. 

The errors introduced by higher wind speeds 
were not those resulting from refraction but 
those from fluctuations of sound intensity owing 
to the gustiness of the wind. These fluctuations 
also are troublesome when there are large tem¬ 
perature inhomogeneities in the air; these are 
especially prominent when the sun is shining 
and the measurements are made over a terrain 
for which the heat absorption varies greatly 
from one area of the terrain to another. At high 
wind speeds the refraction effects were very 
prominent for the ranges of less than 100 m. 
For example, with a wind speed of 2,640 ft per 
min, for horizontal projection of sound at a 
height of 1.5 m and a range of only 50 m from 
the source, the level at various azimuths varied 
from 92 db against the wind to 102 db with the 
wind. 


(^RTdexttam 

























































Chapter 10 

INJURIOUS EFFECTS OF EXPOSURE TO LOUD TONES AND NOISES 


«*■» INTRODUCTION 

E arly in world war ii, a project was orig¬ 
inated at Harvard University under Sec¬ 
tion C-5, NDRC, to study the physiological 
effects of exposure to certain sounds. Later this 
work was transferred to the Committee on 
Medical Research [CMR] and continued under 
their auspices. This report includes the signifi¬ 
cant results from both the Harvard 1 and CMR-’- 3 
reports. 


102 HEARING LOSS PRODUCED IN 
HUMANS 

10-21 Description of Experiments 

The ears of 15 young men (17 to 21 years) 
and of 4 older men (29 to 46 years) were re¬ 
peatedly exposed at intervals of several days 
to intense tones of frequencies of 500, 1,000, 
2,000, and 4,000 c at intensities of 110, 120, and 
130 db for periods of from 1 to 64 minutes. A 
noise of continuous frequency spectrum, some¬ 
what resembling airplane noise, was also em¬ 
ployed. 

Following each exposure, tests were made of 
the threshold of auditory sensitivity and of the 
ability to understand words spoken in an A-9 
oxygen mask, recorded through an MC-254 car¬ 
bon microphone heard through a standard head¬ 
set (Murdock R-14). In many experiments the 
perception of loudness at various intensity 
levels was also measured, and several studies 
were made of the distortion of pitch perception 
(diplacusis). 

Temporary impairment of hearing was regu¬ 
larly produced, but there was no evidence of 
cumulative injurious effects. The only definite 
permanent hearing loss (32 db at 3,400 c) was 
produced by a 20-minute exposure in four 
5-minute periods to 500 c at 140 db. Intensities 
above 140 db can probably be tolerated for 
many seconds without permanent damage, but 
such intensities have not been systematically 


explored with the human ear. At 500 c the pain 
at the eardrum produced by 140 db is definite 
for the first few seconds and then passes off. 
It is less for 1,000 c and 2,000 c. Evidence of 
mild labyrinthine stimulation, especially when 
the tone is turned on and off, appears at about 
140 db. Pain is not an index of the effectiveness 
of a tone in causing deafness. Neither tempo¬ 
rary incapacity from pain or labyrinthine stim¬ 
ulation nor any permanent deafness has been 
produced by exposure to pure tones from 500 
to 2,000 c at 140 db for periods up to 5 minutes. 

Interruption of a tone by brief periods of 
silence (1 to 5 seconds) does not alter its effec¬ 
tiveness in producing hearing loss. One minute 
of exposure to a continuous tone produces sub¬ 
stantially the same hearing loss as 2 minutes 
of exposure to alternate periods of 1 second on, 
1 second off. More rapid interruption decreases 
slightly the hearing loss produced. The discom¬ 
fort from the interrupted tone is greater, how¬ 
ever, than that from the corresponding steady 
tone. 

No significant elevation of auditory threshold 
is produced for tones of frequency lower than 
the exposure tone. The greatest hearing loss 
occurs at a frequency about half an octave 
above the exposure tone. With brief exposures 
the loss may be confined to the two octaves 
above, but with the longer exposures the hear¬ 
ing loss may be quite extensive for all tones 
above the exposure frequency. 


Summary of Results 

Taking as a measure of hearing loss the aver¬ 
age loss throughout the two octaves above the 
exposure tone, it was found that: 

1. 1,000 c and 2,000 c are about equally effec¬ 
tive in producing hearing loss. 

2. 4,000 c is much more effective and 500 c is 
much less effective than 1,000 or 2,000 c. 

3. Hearing loss develops most rapidly during 
the first minutes of exposure and then more and 
more slowly. 


F1DENTLAL 


110 




EXPERIMENTS WITH ANIMALS 


111 


4. More intense tones usually cause greater 
hearing losses, but 1-minute exposures to 
2,000 c may be less effective at 135 db than at 
125 or 130 db. 

5. The complete relations of hearing loss to 
frequency, intensity, and duration are complex. 

6. Recovery of hearing usually begins rapidly 
and then progresses more and more slowly. Re¬ 
covery from a 60-db hearing loss may require 
four or five days to be complete. Recovery tends 
to be slowest for frequencies of about 4,000 c, 
regardless of the frequency of the original ex¬ 
posure tone. 

Some men are much more susceptible than 
others to the production of hearing loss. There 
are differences also as to the part of the fre¬ 
quency range most readily affected, as well as 
in the rate of recovery from a given degree of 
loss. Occasionally any one man may deviate con¬ 
siderably from his usual susceptibility. The 
results of exposure to 2,000 c are more variable 
than for the other frequencies. 

The impairment of hearing produced by ex¬ 
posure to loud tones or noise is of the variable 
or nerve deafness type. In spite of elevations 
of threshold of 50 or 60 db, there may be little 
or no loudness loss for sounds at the 100-db 
loudness level. Losses at this level rarely exceed 
6 db. The audiogram alone is not an adequate 
measure of the impairment of auditory function. 

The modification of loudness perception is 
shown to be more complex and variable than 
has hitherto been described either for nerve 
deafness or for masking with a background 
noise of continuous spectrum. 

Exposure to a pure tone that causes a hearing 
loss that is restricted to a relatively narrow 
range of frequencies may cause very severe 
distortion of pitch perception (diplacusis). 
Tones of certain frequencies sound noisy and 
impure or they may be abnormally elevated in 
pitch by as much as three-quarters of an octave. 
The major displacements of pitch are always 
upward. Exposure to a band spectrum noise 
(like airplane noise), which causes a wide¬ 
spread hearing loss that is usually most severe 
in the high-frequency range, is relatively inef¬ 
fective in producing diplacusis. 

The impairment of understanding of speech 
is more closely related to the overall loudness 


loss at the intensity level at which the speech is 
heard than to the threshold audiogram or to 
loudness loss in any special portion of the 
speech frequency range (400 to 4,000 c). Pro¬ 
longed exposure to an intense 500-c tone or to 
noise of wide frequency spectrum causes severe 
articulation loss at a low (40-db) loudness level 
but only moderate loss at a high (100-db) level. 
The articulation loss for loud speech following 
the 500-c exposure tends to be the greater of 
the two, even though the average hearing loss 
measured by audiogram is less, probably be¬ 
cause of the greater diplacusis produced by the 
exposure to the pure tone. Exposure to an intense 
1,000-c tone may or may not produce a measur¬ 
able articulation loss for loud speech, and ex¬ 
posures to 2,000- and 4,000-c tones cause but 
little articulation loss, even at the 40-db loud¬ 
ness level, for speech heard through a standard 
Army headset. 


10 3 EXPERIMENTS WITH ANIMALS 

Guinea pigs were exposed to pure tones of 
various frequencies at intensities from 140 to 
157 db. The effects of 500 c and 1,000 c were 
most completely explored. Severe and extensive 
damage to the cochlea may be caused by loud 
tones without apparent injury to the eardrum, 
ossicles, or vestibular apparatus. The least de¬ 
tectable anatomical damage to the inner ear, 
i.e., the disappearance of mesothelial cells from 
a limited area of the lower surface of the basilar 
membrane, was produced by 1,000 c at 140 db 
for 3 minutes. More severe and extensive dam¬ 
age is produced by more intense tones and by 
longer exposures, and includes degenerative 
changes in the sensory cells, rupture of the 
organ of Corti, and dislocation of the organ of 
Corti from the basilar membrane. A few days 
or weeks after severe exposure, the organ of 
Corti disappears where it has been severely 
damaged, and the nerve fibers and ganglion 
cells degenerate. 

The milder degrees of damage are localized, 
but a very severe exposure (150 db for several 
minutes) causes widespread permanent dam¬ 
age. The damage tends to be located nearer the 
helicotrema when caused by low tones and 




112 


INJURIOUS EFFECTS OF EXPOSURE TO LOUD TONES 


nearer the oval and round windows for high 
tones. 

The electrical activity of the cochlea (Wever 
and Bray effect or aural microphonics) is im¬ 
paired by exposures which cause definite ana¬ 
tomical changes in the inner ear. There is some 
general correspondence between changes in the 
electrical audiogram and the anatomical dam¬ 
age, but the parallelism is not exact or invari¬ 
able. The anatomical changes are the more 


consistent, and it is believed that the electrical 
audiogram is not so satisfactory or reliable a 
method of assessing injury to the ear as micro¬ 
scopic examination. 

These experiments with animals probably 
demonstrate the nature of the injury to human 
ears that would be produced by sufficiently in¬ 
tense continuous sounds, but they do not indi¬ 
cate the intensities or durations of exposure 
necessary to produce such injury in man. 






Chapter 11 

HIGH-INTENSITY SOUND PRODUCED BY CHAIN EXPLOSIONS 


111 INTRODUCTION 

V ARIOUS DEVICES have been proposed for the 
production of a sound of sufficient intensity 
to disrupt auditory communication over a large 
area. This chapter treats the theoretical prob¬ 
lem of covering an area of 1 sq mile with a 
minimum sound intensity of 120 db by detonat¬ 
ing a series of small explosive charges. 

The calculations in this study 1 were based on 
measurements of the pressure level and dura- 


problem of forming a continuous sound from 
unit explosions, special consideration was given 
to the time interval between detonations which 
will yield the highest efficiency from the ex¬ 
plosive material. 

In Table 1 the first three lines show the basis 
of choice of the interval used in the calculations. 
The first line shows the total duration of the 
first three pulses, which contain nearly all of 
the acoustic energy, of an explosion at a dis¬ 
tance of 1,100 ft. The third pulse in some in- 


Table i 



Wave 

combi¬ 

nation 

Weight per charge (lb) 

1/4 

1/2 

1 

2 

4 

8 

16 

Group 1 

3/2 

19.7 

25.8 

25.3 

33.9 

37.8 

45.0 

48.9 

Duration at 1,100 ft 

5/4 

14.4 

16.7 

19.4 

21.1 

25.0 

30.5 

37.8 

(msec) 

33.3 

33.3 

33.3 

33.3 

33.3 

33.3 

33.3 

33.3 

Group 2 









Pressure levels in db 

3/2 

118.53 

122.19 

126.79 

128.99 

132.40 

132.98 

135.16 

above 0.0002 dynes 

5/4 

‘ 120.70 

124.72 

128.61 

131.83 

135.28 

135.54 

135.75 

per sq cm corrected 

33.3 

116.31 

121.06 

125.68 

128.99 

133.26 

135.08 

137.56 

to 1,000 ft 









Group 3 









Distance at which 

3/2 

887 

1,183 

1,684 

1,994 

2,591 

2,708 

3,187 

pressure level is 120 

5/4 

1,053 

1,437 

1,936 

2,480 

3,232 

3,297 

3,350 

db = radius of 120- 

33.3 

753 

1,085 

1,547 

1,994 

2,767 

3,183 

3,850 

db circle (ft) 









Group 4 

3/2 

2.47 

4.40 

8.91 

12.49 

21.1 

23.1 

31.9 

Area of 120-db circle 

5/4 

3.48 

6.49 

11.77 

19.32 

32.8 

34.1 

35.3 

X 10+6 sq ft 

33.3 

1.78 

3.70 

7.52 

12.49 

24.0 

31.8 

46.6 

Group 5 

3/2 

5.14 

4.40 

4.42 

4.72 

5.01 

7.70 

10.25 

Lb per sq ft per sec 

5/4 

5.02 

4.61 

4.36 

4.90 

4.88 

7.68 

12.00 

X 10-6 

33.3 

4.22 

4.06 

3.98 

4.80 

5.00 

7.55 

10.30 


tion of single explosions of various weights of 
dynamite. Sound level meters do not give true 
indications of actual pressure levels, either in¬ 
stantaneous or rms, such as can be derived 
from analysis of oscillograms, but properly used 
they yield useful comparative data. 


11 2 METHODS OF COMBINING UNIT 
EXPLOSIONS 

The wave forms of explosive sounds are il¬ 
lustrated in Section 12.1. In the theoretical 


stances dips near the neutral line without cross¬ 
ing it. In these cases that portion of the pulse 
which lies beyond the arbitrary termination of 
the curve has been neglected. The durations of 
the first two pulses increase with distance from 
the source. All pressure levels have been cor¬ 
rected to 1,000 ft. 

The duration shown in the second line is the 
interval between the beginning of the explosion 
and the peak of the second positive pressure 
pulse. If all pulses were of equal duration, this 
would be the period of five-fourths of one cycle 
and has been (loosely) so designated. 




113 



















114 


HIGH-INTENSITY SOUND PRODUCED BY CHAIN EXPLOSIONS 


In the third line an interval of 33.3 millisec¬ 
onds between detonations has been arbitrarily 
selected. 

Figures 1, 2, and 3 illustrate the three meth¬ 
ods of combining individual detonations de¬ 
scribed above to form continuous sound. The 



Figure 1. The “3/2-cycle” method of combining 
explosions to form continuous sound. 


combinations shown have been formed from the 
oscillogram of the wave resulting from explod¬ 
ing a 14 -lb charge of dynamite. 


11 3 INTENSITY AND RATE OF 
ATTENUATION 

The second group of three lines in Table 1 
shows the pressure levels in decibels above 



Figure 2. The “5/4-in.-cycle” method of com¬ 
bining explosions to form continuous sound. 

0.0002 dyne per sq cm at a distance of 1,000 ft, 
derived from the above wave combinations. 
These are the theoretical intensities at 1,000 ft 
derived from the respective wave combinations 


above described and with the various weights 
of charges shown. 

The third group of three lines shows the dis¬ 
tance from the source at which the intensity 
will be 120 db, assuming 9 db attenuation per 
distance doubled. The rate of attenuation per 
distance doubled is a variable depending upon 
the frequency spectra of the sound, the coeffi¬ 
cient of absorption of the terrain, and the dis¬ 
tance from the source. The attenuation due to 
absorption varies directly as the distance, so 
that in doubling a large distance the absorption 
is greater than in doubling a small one. The 
average rate of attenuation of gun and simu¬ 
lant sounds observed between 1,500 and 8,700 
ft, using General Radio sound level meters at 
Fort Bragg, the terrain being sandy soil cov¬ 


SMALL CHARGES 



Figure 3. The “33.3-millisecond” method of 
combining explosions to form continuous sound. 

ered with thin grass and occasional low shrub¬ 
bery, in clear summer weather, was 9.9 db. The 
average attenuation observed at Pine Camp in 
measuring two-cycle motor sounds at distances 
ranging from 1,000 ft to 2 miles was 8.9 db. 

The fourth group shows the areas of the cir¬ 
cles corresponding to the radii designated in 
the third group. Each circle represents the area 
within which the intensity will not be less than 
120 db. 

The fifth group indicates the number of 
pounds of explosive per second per square foot 
required to give 120 db at the periphery of the 
circles with various weights of unit charges. 
The values shown in the fifth group have been 
used as a “figure of merit” in choosing the 
weight of explosive per charge and time inter- 
























































SUMMARY AND EVALUATION 


115 


val between charges to be used in an acoustic 
bomb. 

The lowest number of pounds of explosive 
per square foot per second shown in Group 5 is 
3.98 X 10~ 6 . This value is derived from explod¬ 
ing 1-lb charges of dynamite at intervals of 33.3 
milliseconds. 

The reason for the rapid increase in the num¬ 
ber of pounds of explosive per square foot per 



120 DB CONTOUR ABOUT SEVEN I—LB 
CHARGES SPACED FOR MAXIMUM COVERAGE 


Figure 4. Equal intensity contours. 

second with increased charges stems from the 
fact that the rate of attenuation is assumed to 
be 9 db rather than 6 for each doubling of the 
distance, while the increase in intensity from 
doubling the charge approximates 3 db. Also 
the larger the circle, the greater the intensity 
at the source, and, since 120 db is adequate to 
disrupt communications, greater intensity the¬ 
oretically adds no advantage but consumes extra 
energy. It therefore appears that the smaller 


the circle, the more efficient the use of the 
explosive. 

There is a lower practical limit to the size of 
the charges. This will be determined by the 
lower practical limit of the distance between 
bombs, bearing in mind that these must be 
placed by dropping from the air. This lower 
practical limit between bombs rather than the 
variation in efficiency with variation in the 
weight of the charge may prove to be the final 
factor in determining the weight selected for 
the individual charge. 

The efficiency of a bomb composed of 31 / 2 -lb 
charges was compared with that of seven 
bombs composed of i/ 2 -lb charges. By calcula¬ 
tion it was determined that a bomb of 3!/2-lb 
charges -firing at 33.3 millisecond intervals will 
cover a circle with 120 db or more having an 
area of 21.302 X 10 G sq ft. A bomb of 14-lb 
charges will cover a circle of 3.697 X 10 s sq ft. 
Seven such bombs used separately will cover 
25.879 X 10° sq ft or an increase of 19 per cent. 
If seven bombs are used in a group as shown in 
Figure 4, the area covered by the seven is cal¬ 
culated to be 35.71 X 10° sq ft or 67.5 per cent 
more than covered by a single bomb of the same 
weight of explosive. 

" 4 SUMMARY AND EVALUATION 

It is concluded that an area equal to 1 sq mile 
may be covered with an intensity of not less 
than 120 db by detonating three acoustic bombs 
spaced 3,868 ft apart, each bomb consisting of 
multiple charges of dynamite, or its equivalent, 
each charge weighing 1 lb, fired at the rate of 
30 per second. The weight of explosive per 
square mile per minute is estimated to be 5,400 
lb, and the weight of explosive per bomb—each 
bomb being capable of 10 minutes’ continuous 
operation—is 18,000 lb. 

It is apparent that under almost all circum¬ 
stances the same weight of explosive used in 
the normal manner will be more effective than 
the acoustic bomb. It is conceivable, however, 
that under some conditions the acoustic bomb 
may be justified even at its high cost. 

No consideration is given herein to the nu¬ 
merous design problems connected with con¬ 
structing an acoustic bomb. Not only must all 













116 


HIGH-INTENSITY SOUND PRODUCED BY CHAIN EXPLOSIONS 


detonations occur in their time sequence with 
great accuracy, but at the instant of detonation 
each charge must be sufficiently removed from 
the undetonated charges to avoid either destroy¬ 


ing or detonating them. The cost of production 
and the complexity of handling are two further 
factors imposing lower practical limits on the 
size of the charges. 


li^^^NTIALj 








Chapter 12 

SOUND SIMULATION AND MASKING 


12 1 SIMULATION OF SMALL ARMS 
AND ARTILLERY FIRE: “CHARLIE” 

T he work described in this section 1 was 
undertaken at the request of the Navy, the 
original object being to provide a package, 
weighing not more than 4 lb and suitable for 
attachment to an airborne dummy paratrooper, 
which would simulate mixed machine gun and 
rifle fire for a period of 10 minutes. The work 
was later continued at the request of the Army. 
Simulants were then designed for both air and 
ground placement, under less rigid specifica¬ 
tions with respect to weight. Mortars of 60 and 
81 mm and, later, guns of heavier caliber were 
simulated. 

The dummy paratrooper has been referred 
to in both Navy and Army circles as “Oscar.” 
The sound-simulating device became known as 
“Charlie.” As the caliber of guns simulated has 
been extended, the name “Charlie” has re¬ 
mained. As herein used, “Charlie” is a deceptive 
general term used to designate specific devices 
for simulating: 

1. Rifle and machine gun fire: .30 and .50 
caliber; 

2. Mortar fire: 60 and 81 mm; 

3. 90-mm guns; 

4. 105-mm howitzers; 

5. 155-mm howitzers; 

6. 155-mm guns. 


1211 The Character of Explosive 
Sounds 

Preparatory to the selection or design of 
appropriate simulants, consideration was given 
to the nature of the sounds to be imitated. 
Oscillograms of the time pressure wave of the 
guns and their simulants were photographed 
with a 35-mm camera. The sweep circuit was 
triggered by energy from a microphone. A sec¬ 
ond microphone was used to energize the verti¬ 
cal circuit of the oscilloscope. The sweep circuit 


microphone was placed 1 to 3 ft nearer the sound 
source than the sound pressure microphone. 

Figure 1 is an oscillogram of a 90-mm gun 
and 1 lb of TNT taken at a distance of 1,500 ft 
from the source. These oscillograms of explo¬ 
sions are typical in that the initial pressure 
rises rapidly and is usually capped by a sharp 
peak. Some fluctuations in pressure, however, 
are evident near the peak. With dynamite the 




Figure 1. Oscillogram of 90-mm gun and its 
simulant at 1,500 ft. 

pressure of the first fluctuation drops abruptly 
to the vicinity of the neutral pressure line, the 
oscillogram thus forming an initial sharp sliver. 
At greater distances the sharp peak sometimes 
becomes a flat jagged top as shown in the oscil¬ 
logram of the 105-mm howitzer and its simulant 
in Figure 2. The negative pressure portion of 
the first cycle is usually more rounded and con¬ 
tains more energy than the positive pressure 
portion. The second positive pressure pulse is 
less intense than the first, is more rounded, and 
usually flattens as it approaches the axis of 


117 




118 


SOUND SIMULATION AND MASKING 








Figure 2. Oscillograms of field pieces and their simulants at 2,900 yd. 






















































SIMULATION OF SMALL ARMS AND ARTILLERY FIRE 


119 


neutral pressure. At distances of the order of 
1,500 ft nearly all the acoustic energy is in these 
first three pulses. At greater distances the pat¬ 
tern becomes more complex, as shown in Fig¬ 
ure 2 taken at a distance of 2,900 yd. There is 
sometimes a rather irregular series of the sec¬ 
ondary waves that fall off quite rapidly in in¬ 
tensity. The latter portions of the oscillograms 
may be much confused by echoes, reflections, 
and refractions of the original. At still greater 


some impression of pitch and can usually say 
that one gun sounds “higher pitched” than 
another. 

The total duration of a muzzle blast increases 
with distance from the source and with in¬ 
creased weight of the propellant. In general, 
the explosive sounds of guns ranging in caliber 
from 90 to 155 mm at a distance of 1,000 ft 
have a duration of approximately 30 millisec¬ 
onds. At 2,900 yd the duration is of the order 


Table 1 





Sound level meters 

db rms 





(db) 


fi-om 


Weight of 


GR 

GR 

ERPI 

oscillo¬ 


propellant or simulant 

Distance 

247 

623 

15 

scope 

.30-cal machine gun, single 
shots only 

Simulant 

Army special cap and 

855 ft 

54.0 

51.0 

71.0 



6 in. Primacord 






.50-cal machine gun, single 


855 ft 

64.5 

65.5 

73.0 


shots only 

Simulant 

Army special cap and 

855 ft 

64.7 

68.0 

72.0 



12 in. Primacord 






60-mm mortar 

0.01 to 0.1 lb 






Simulants 

lb dynamite, TNT, ox- 

1,003 ft 

86.5 

82.0 

93.5 



20 ft Primacord 






81-mm mortar 

0.1 to 0.5 lb 






Simulants 

% lb dynamite, TNT, or 

1,003 ft 

86.5 

82.0 

93.5 



20 ft Primacord 






90-mm gun 

7.31 lb NH powder 

2,900 yd 

69.0+ 

68.0 

92.0 

93.2 

Simulants 

2 lb TNT or IV 2 lb C2 

2,900 yd 

69.0— 

68.0 

91.5 

90.5 

105-mm howitzer 

3.04 lb FHN powder 

2,900 yd 

81.5 

78.5 

95.5 

94.5 

Simulant 

% lb TNT 

2,900 yd 

79.5 

79.0 

95.0 

92.3 

155-mm howitzer 

7.8 lb 

2,900 yd 

81.5 

82.0 

91.0 

94.5 

Simulants 

2 lb TNT or 1 % lb C2 

2,900 yd 

82.0 

84.5 

93.5 

96.7 

155-mm gun 

22 lb 

2,900 yd 

80.0— 

82.0 

96.5 

95.86 

Simulants 

8 lb TNT or 6 lb C2 

2,900 yd 

78.5 

80.5 

97.5 

95.9 


distances, however, the wave becomes simpli¬ 
fied due to the fact that high frequencies are 
attenuated more rapidly than the lows, causing 
the sound energy to approach a sine wave in 
form. The durations of the first two pulses also 
change with distance; both become longer as 
they proceed from the source. 

The train of one positive, one negative, and 
another positive wave, all of different dura¬ 
tions, is too brief and irregular to establish any 
clear impression of frequency, and the sense 
of pitch of gun sounds is therefore rather in¬ 
determinate. A listener does, however, obtain 


of 60 milliseconds. However, an observer will 
hear echoes following a gun blast for periods 
ranging up to 0.5 second or more. Their dura¬ 
tion is dependent upon the terrain, particularly 
upon echoing surfaces, and the rate of absorp¬ 
tion. The echoes leave a marked impression on 
the observer as to the nature of the sound 
heard, probably because the duration of the 
echoes is long compared with that of the orig¬ 
inal blast. Since the echoes are a function of 
terrain, the sound of the muzzle blast is, there¬ 
fore, also a function of terrain as well as of the 
propellant and gun. 


FIAL 


























120 


SOUND SIMULATION AND MASKING 





Figure 3. Two pressure waves A and C of muz¬ 
zle sounds of 155-mm howitzers taken 15 minutes 
apart; also two pressure waves B and D of simu¬ 
lants, each taken within 5 seconds of the sound 
imitated. All measurements 2,900 yd from source. 

Simulation of Single Shots: 

Wave Form 

The transient character and high intensity 
of muzzle blasts make them very difficult to imi¬ 
tate by any mechanical or electroacoustic de¬ 
vice. It was soon realized that by far the best 


simulant of an explosive sound is another ex¬ 
plosive sound. The sounds of various explosive 
simulants were, therefore, studied by means of 
oscillograms, sound level meters, and listening 
tests and compared with corresponding data 
concerning the sounds of muzzle blasts. 

The simulants finally selected as most appro¬ 
priate for various guns and field pieces are 
tabulated in Table 1. Each field piece and the 
weight of propellant employed is listed, to¬ 
gether with the weight and nature of the ex¬ 
plosive used as a simulant. Also listed are the 
intensities of both the muzzle blast and its 
simulant as recorded by three different sound 
level meters and also as determined from oscil¬ 
lograms. The measurements of noise level pro¬ 
duced by explosive sounds differ systematically 
depending on the sound level meter employed. 
The two General Radio meters do not differ 
systematically one from the other, but the dis¬ 
crepancy between them and the Electrical Re¬ 
search Products, Inc. [ERPI] instrument was 
as much as 20 db on some waves. The discrep¬ 
ancy may be caused by differences in the over¬ 
load characteristics of the amplifier and rectifier 
circuits, and by differences in the time con¬ 
stants of the circuits and, possibly, of the indi¬ 
cating instruments. 

In most instances oscillograms of the muzzle 
blast and its simulant show striking similarity 
when the two are taken a few seconds apart. 
Figure 2 shows oscillograms of a 90-mm gun, 
105-mm howitzer, 155-mm howitzer, and 155- 
mm gun paired with oscillograms of their simu¬ 
lants. All of these oscillograms were taken at a 
distance of 2,900 yd from the guns and simu¬ 
lants. The oscillogram of the simulant was 
taken within 5 seconds of that of the original. 
While there are plainly some variations be¬ 
tween the original and the simulant, the simi¬ 
larities are certainly more impressive than the 
differences. 

Figure 3 shows two oscillograms of a 155-mm 
howitzer taken 15 minutes apart, together with 
corresponding oscillograms of its simulants. 
The simulants were photographed in each in¬ 
stance within a few seconds of the original. It 
is apparent that the simulant is more like the 
original in each case than the two originals are 
like each other. 



CONFIDENTIAL ] 







SIMULATION OF SMALL ARMS AND ARTILLERY FIRE 


121 


These observations indicate that sound un¬ 
dergoes marked changes in transmission, that 
the conditions which affect transmission vary 
through wide limits in a very few minutes, and 
that any given set of conditions influence the 
sound of the guns and of the simulants in much 
the same manner. 

1213 Simulation of Single Shots: 

Intensity 

It is, therefore, clear that simulation of 
muzzle blast by other explosions is satisfactory 
as to wave form. Simulation in regard to inten¬ 
sity is equally satisfactory, largely because 
there is no fixed value of intensity which must 
be closely matched. Most field pieces are sup¬ 
plied with several propellants differing in 
weight and therefore in the intensity of their 
muzzle blast. Each piece has therefore not one, 
but several intensities of blast which are typi¬ 
cal, and, even when a charge of given size is 
fired by a given field piece at a given location 
and an auditor listens at a fixed location at some 
distance, the sound which reaches him varies 
from shot to shot due to variations in the trans¬ 
mission characteristics of the atmosphere. Each 
small change in density of the air, which is 
stirred by many gusts of wind, offers a varia¬ 
tion in reflection and refraction. Oscillograms 
taken of a field piece at various times at a given 
location show quite marked differences not only 
in wave form but also in intensity. The imita¬ 
tion of gun sounds is not a problem of imitating 
a constant sound but rather a sound which 
varies within rather wide limits of intensity 
and wave form. It is, therefore, understandable 
why simulants give most impressive imitations 
of explosive sounds whereas some other sounds, 
particularly speech, have been found most diffi¬ 
cult to duplicate. 

The sound of gun fire can be successfully imi¬ 
tated by the use of nitrostarch, Primacord, 
dynamite, TNT, or C2. In general, the weight of 
the simulant required is about a quarter to a 
half the weight of the propellant due to the fact 
that much of the energy of the propellant is 
absorbed in accelerating the projectile. Equiva¬ 
lent weights of the above explosives for gener¬ 
ating acoustic power are given in reference la. 


Listening Tests 

Listening tests conducted by trained person¬ 
nel indicate that the ear cannot detect the dif¬ 
ference between the muzzle blasts of the various 
field pieces and the appropriate simulants se¬ 
lected. 

The simulant for a .50-caliber gun has been 
tested with particular care. Thousands of 
rounds were fired in the presence of several 
hundred Army observers. Even trained ob¬ 
servers failed to detect any difference between 
actual machine gun fire and its simulant. It 
was the consensus that the sounds produced by 
Primacord are fully authentic and so similar to 
actual gun sounds that detection of any differ¬ 
ence by ear is quite impossible. 

Detection by Sound-Ranging 
Equipment 

Although the similarity between the sounds 
of a muzzle blast and of its simulant is entirely 
satisfactory over most of the audio range, dif¬ 
ferences occur in the low-frequency range for 
90-mm guns and pieces of larger caliber, of suf¬ 
ficient intensity to be detected by Army sound¬ 
ranging equipment. The difference permitted 
the observer to distinguish successfully between 
the simulant and the actual gun under the cir¬ 
cumstances of the test, i.e., when gun and simu¬ 
lant were fired at the same place. If variations 
in distance and complications due to multiple 
firing were introduced, however, it is doubtful 
whether or not consistent detection could be 
made. 

An important distinction should be made, 
nevertheless, between the sound of the muzzle 
blast of a field piece and the entire sound of the 
field piece which consists of the muzzle blast, 
the projectile sound, and the burst of the shell. 
In the case of heavy field pieces, deception can 
succeed only when the simulants are used in 
connection with real pieces. Projectile sounds 
and shell bursts in enemy territory must add 
their necessary realism in order to deceive. If 
some of these additional sounds are provided, 
however, and if the usual care and skill neces¬ 
sary in most deceptive efforts are exercised, it 
should at least be possible to deceive the enemy 


CONFIDENTTJSBPt 






122 


SOUND SIMULATION AND MASKING 



as to the number of field pieces present. The 
simulants may also serve to confuse the op¬ 
erators of sound-ranging equipment and there¬ 
by diversify the enemy’s return fire. 


12 16 Simulation of Machine Gun Fire 

Imitation of the sound of machine guns re¬ 
quires not only successful duplication of the 
sound of a single shot but also duplication of the 
rate and regularity of fire of an actual weapon. 
The appropriate timing of the explosions of 
successive charges of the simulant has been ob¬ 
tained by detonating the charges of Primacord 
by electric caps attached to a timer made from 
a telephone dial and energized by a dry cell. The 
telephone dial is set with its dial turned as far 
as possible in the clockwise direction and re¬ 
tained in this position by a piece of fuze. When 
this fuze is ignited, either by means of a slower 
timing fuze or by electric control, the dial is re¬ 
leased and fires the ten charges of Primacord in 
rapid succession as it returns to its home posi¬ 
tion. 

The individual charges are mounted on a 
stick to keep them sufficiently separated one 
from another and thus avoid interaction be¬ 
tween them. These devices may be fired from 
the ground or dropped on a small parachute 
from an airplane. Figure 4 is a photograph of 
such a machine gun simulator. The complete 
details and instructions for making and using 
this device are contained in reference lb. 


Desultory Rifle Fire 

The original objective of the Navy was to 
secure a device which would simulate desultory 
rifle fire over a period of 10 minutes. To provide 
this distribution in time, four packages each 
containing 25 individual charges of the appro¬ 
priate length of Primacord were formed into a 
single larger package to be thrown from an air¬ 
plane. When the large package is thrown from 
the plane, its outside wrapper is torn off by the 
rip cord. A pull-wire lighter ignites the fuzes of 
the various unit packages and also opens four 
small parachutes, one for each of the small 


Figure 4. Machine gun simulator. 


CONFIDENTIAL * 









123 


SIMULATION OF MOTOR SOUNDS: “CANARY” 


packages. The four units float to the ground, 
and the various charges detonate at intervals 
determined by the lengths of their respective 
fuzes. Each package is timed with an appropri¬ 
ate length of fuze, the fuze lengths differing so 
as to cause the packages to begin firing in 10 
seconds, 2V£ minutes, 5 minutes, and 7*4 min¬ 
utes respectively after they have been dropped 
from the plane. In each of the smaller packages 
the 25 lengths of Primacord are mounted 
around a spreader charge. The spreader charge 
is timed to fire first. When it explodes, it scat¬ 
ters the 25 rounds of Primacord over an area 
approximately 50 ft in diameter. The fuze of 
each round is ignited before the spreader 
charge explodes, and each charge detonates 
when the fire in the fuze reaches its cap. The 
fuzes of each unit package are cut to various 
lengths to provide desultory fire over a period of 
214 minutes. 

Full details and instructions for the manu¬ 
facture and for the operation of this device are 
also completely described in reference lb. 


12-1,8 Simulation of Mortar Fire 

In Table 1 it will be observed there is a wide 
range of simulators for 60- and 81-mm mortars. 
The variety corresponds to the different 
weights of the propellant used in these mortars. 

Reference lb also describes complete details 
for making and using a package that will simu¬ 
late six rounds of mortar fire. This package is 
suitable for dropping from the air without a 
parachute. The timing of the explosion of the 
successive charges is determined by the length 
of the fuze attached to each. When the package 
is thrown from the plane, the cover is ripped 
open by the static cord. The six fuzes are ignited 
by pull-wire lighters, and the charges fall sepa¬ 
rately to the ground. The timing of the shots 
has been made to simulate to some degree the 
timing of the mortar fire. The package de¬ 
scribed 11 ’ is timed to fire its charges at approxi¬ 
mately 10, 13, 16, 17, 18, and 19 seconds respec¬ 
tively after dropping from the plane. The tim¬ 
ing can, of course, be changed as desired, simply 
by changing the lengths of the fuzes. 


121,9 Simulation of Larger Field Pieces 

Table 1 gives the weight and kind of simu¬ 
lants for the 90-mm gun, the 105-mm howitzer, 
the 155-mm howitzer, and the 155-mm gun. If 
TNT or C2 is not available, appropriate weights 
of dynamite or nitrostarch may be substituted 
in amounts indicated in reference la. It is in¬ 
tended that simulants for these large field pieces 
be fired individually, probably coordinated with 
the fire of actual field pieces. There is no special 
problem of timing corresponding to the timing 
of machine gun fire or mortar fire. 

The simulation of small arms and of the 
muzzle blasts of artillery fire by means of the 
explosion of charges of appropriate weights of 
nitrostarch, TNT, dynamite, Primacord, or C2 
may be considered entirely satisfactory as far 
as pure acoustic imitation is concerned, acoustic 
simulation being easy and complete (except as 
against sound-ranging equipment sensitive to 
very low and subaudible frequencies). A weight 
of high explosive equal to about one-half or one- 
third the weight of the propellant is quite ade¬ 
quate, and its effectiveness is not critically de¬ 
pendent on the choice of explosive. It is recog¬ 
nized, however, that any simulation to be fully 
effective must be complete and consistent. Vis¬ 
ual as well as acoustic aspects must be consid¬ 
ered also, and the final choice of explosive 
should be based on appropriate simulation of 
flash and smoke as well as of sound. 


122 SIMULATION OF MOTOR SOUNDS: 

“CANARY” 

The “Canary” 10 consists of two small out¬ 
board motors each equipped with an acoustic 
horn. The two are operated together at slightly 
different speeds to give a beat note of low fre¬ 
quency. The sound of the Canary may be em¬ 
ployed for deceptive purposes, with a range of 
2 to 4 miles over land and considerably more 
over water. It has been variously pronounced to 
sound like airplanes, tanks, or steam shovels. 
The Canary is also particularly effective as a 
masking device to obscure the sounds of mili¬ 
tary vehicles. 




124 


SOUND SIMULATION AND MASKING 


Description 

The motors used in both the experimental and 
field model Canaries were Johnson outboard 
type POLR-15 of 22 hp. Each has two cylinders 
in opposed relation, both of which fire simul¬ 
taneously in order to attain the greatest acous¬ 
tic intensity. 

A horn is attached to the two exhausts of 
each motor. Each horn has two throats as 

k 

< 




Figure 5. Diagram of Canary horns. 


shown in Figure 5. The horn was designed for 
a theoretical cutoff of 100 c. It is exponential in 
expansion rate and rectangular in cross sec¬ 
tion. It is 54 in. long, the total area at the throat 
being 7.57 sq in. and the total area at the mouth 
being 1,142 sq in. 

The experimental models of the Canaries 
were mounted on water tanks and operated 
with their propellers in the water, to provide an 


appropriate load. In the field model shown in 
Figure 6 the propellers and their driving rods 
were removed and replaced with hydraulic 
brakes. 

The brake is bolted to the motor head. The 
diameter of the rotor is 5 in., and the inside 
diameter of the stator is 5Vs in. Five blades are 
attached to each face of the rotor and four to 
each face of the stator. The brake absorbs 22 hp 
at 4,000 rpm. a 

Cooling is provided by radiators of tubular 
fin construction 15 in. wide, 17 in. long, and 6 
in. deep. The total area is 12,240 sq in. for each 
motor. Cooling water is circulated by the hy¬ 
draulic brake. Air is delivered by a blower 
wheel driven by an extension of the brake shaft 
through a 10 to 7 gear reduction. The blower 
wheel (manufactured by the Torrington Manu¬ 
facturing Co.) has a capacity of 2,400 cu ft per 
minute at 2,500 rpm. 

The weight of the field model, exclusive of the 
carrier, is 800 lb, consisting of two units of 300 
lb each and a pivot and frame weighing 200 lb. 
The weight of each unit is made up as follows: 


Motor head and fuel tank, dry 

65% 

lb 

Brake, dry 

21 

lb 

Radiator, dry 

60 

lb 

Horn 

123 

lb 

Fuel 

15 

lb 

Water 

15% 

lb 

Total 

300 

lb 


The field model is satisfactorily mounted on the 
bed of a light truck. 


12 - 2 - 2 Operation 

The motor governors do not regulate the 
speeds of the motors with complete constancy, 
and consequently they vary in speed between 
narrow limits. These variations of speed are 
sufficient to generate a continually changing 
beat note which imparts an interest-compelling 
character to the sound and greatly improves its 
abilities to mask the sound of vehicles. The 
characteristic “putt-putt” of the outboard 

a It is anticipated that the details of design of this 
hydraulic dynamometer, developed for this project, will 
be cleared and published in an appropriate technical 
journal. It is, therefore, unnecessary to present further 
details here. 


CONFIDENTIAL \ 







































125 


SIMULATION OF MOTOR SOUNDS: “CANARY” 


motor is no longer obvious to a listener. Since 
the high frequencies are attenuated with trans¬ 
mission more rapidly than the lows, the low fre¬ 
quencies increasingly predominate with in¬ 
crease in distance. 

A wide variety of modifications of the sound 
of the Canary may be obtained: (1) by using a 
chopper rotating in front of the horn or at a 
point between the throat and the mouth of the 
horn; (2) by means of a “butterfly,” a rectan¬ 
gular hole cut in the side of the horn at a point 
1 or 2 ft from the horn throat and equipped 
with a flat metal plate that rotates to alternately 



Figure 6. Canary: field model. 

open and close the opening; (3) by variations in 
the absolute speeds of the motors; and (4) 
changes in the direction of the beam. 

Both the chopper and the butterfly serve to 
modulate the intensity by 6 or 8 db, but neither 
feature was incorporated in the field model. One 
limitation on the manual operation of any such 
modulations lies in the necessity of carrying 
them out with an accuracy consistent with the 
gradual changes of speed of a large machine. 
When used for deceptive purposes, the Canary 
suggests a large machine because of the pres¬ 
ence of the low-frequency beat, and any modu¬ 
lation must be consistent with this illusion. 
Manual control should therefore be attempted 
only by practiced personnel with a high sense 
of rhythm and timing. It is anticipated that the 
chief modification in practice will be in the di¬ 
rection of the beam which automatically 


changes the intensity of sound delivered to any 
particular distant point. 


Acoustic Performance 

The pressure level of a Canary (two motors) 
is 123 db at 100 ft in front of the horns. Figure 


1- 
























































K 

> 



! 













1 

1A> 

IEC 

(IN 

: t 

1U 

■ \ 

IN/ 

1 



4 


J 


» 



\ 








> 

1- 

1 MINIMUM 

N NO. OF 01 

1 1 1 II 

3: 

LI 

5ERVAT 

J 

IONS 

L 

1 





K 

2 ' 









100 1000 10.000 100,000 
DISTANCE IN FEET 


Figure 7. Sound transmission of Canary over 
thick grass 18 in. high, occasional trees. Data 
taken under both day and night conditions over a 
period of several weeks. 


7 shows the relation between pressure level and 
distance over land. The measurements were 
taken over a period of several months under 
varying but unclassified weather conditions. 



Figure 8. Sound transmission of Canary over 
water. 


Figure 8 shows the relation between pressure 
level and distance over water at night. Figure 9 
shows the frequency distribution of the acoustic 
energy of a single motor between 60 and 900 c. 

The pressure level varies by 10 db as the 


XFIDENT1AL 































































































126 


SOUND SIMULATION AND MASKING 


speed of the motor is increased from its normal 
speed range from 2,400 to 4,200 rpm. At high 
speeds one motor sounds somewhat like a siren. 

The attenuation of Canary sounds trans¬ 
mitted over sandy soil with thick grass in the 
daytime is approximately 9 db per distance 
doubled. In normal weather conditions the de¬ 
ceptive quality is best at between 2 and 4 miles 
over land and between 3 and 15 miles over 
water. Deception is most effective when the 


The Canary, originally developed as a decep¬ 
tive sound source, and the Bell Telephone Labo¬ 
ratories’ [BTL] siren both proved to be prac¬ 
tical means of generating such a sound screen. 
Their effectiveness was tested experimentally, 
and an analysis was made of acoustic data to 
determine the character, number, and position 
of the masking devices required to conceal any 
given movement of a specified group of ve¬ 
hicles. 1 ' 1 



Figure 9. Single motor of Canary. Portion of 
frequency spectrum between 70 and 900 c. 


Sound of Moving Vehicles 

Measurements were made of the intensity 
and the frequency spectrum of the sounds of the 
following Army tanks: M3A1, M3A5, M4A1, 
M4A3, M5A1, and M10, and also of the 2 1 / 4-ton 
truck and the lV->-ton personnel carrier. The in¬ 
tensity varies 4 to 9 db with the azimuth of the 
observer and is usually loudest directly behind. 
Ninety to 95 per cent of the energy lies between 
65 and 300 c. It is the exhaust sounds, particu¬ 
larly at distances of 1/2 mile or greater, that 
usually determine the amount of masking noise 


sound can be distinctly heard through ambient 
noises but not with sufficient loudness to give a 
clear impression of the character of the sound. 


123 THE SOUND SCREEN: MASKING 
THE SOUNDS OF MILITARY VEHICLES 

It is often desirable to conceal from the 
enemy the movement of military vehicles such 
as tanks, trucks, and personnel carriers. Visual 
detection may be prevented by taking advan¬ 
tage of favorable features of terrain, such as 
hills or embankments, by the use of smoke 
screens, or by carrying out the movement under 
cover of darkness. But, although the vehicles 
are no longer visible, they remain audible, and 
the present problem is to devise a means of pre¬ 
venting detection of the sounds of military 
movement or action. The objective is accom¬ 
plished by providing a somid screen, that is, an¬ 
other sound that masks the sound of the ve¬ 
hicles, rendering them inaudible just as a 
smoke screen renders them invisible. 



NUMBER OF TANKS 

Figure 10. Increase in the intensity at the ob¬ 
servation post due to the sound of N vehicles, 
arranged as shown in sketch, over the intensity 
due to a single vehicle at 133 yd. Based on: 9 db 
loss per distance to vehicles doubled. 

required to prevent the detection and recogni¬ 
tion of tank sounds. At shorter distances the 
track noises are sometimes prominent. The 
addition of more efficient mufflers would greatly 
facilitate masking and improve the chances of 
successful surprise attack. 

At 100 ft the pressure level of the sounds 
from the above vehicles varies between 80 and 






















































MASKING THE SOUNDS OF MILITARY VEHICLES 


127 


108 db for the various tanks and between 70 
and 85 for the trucks. The intensity varies, of 
course, with the type of motor, the horsepower, 
the exhaust system, and also the motor speed 
and load. 


Sound Intensity of Groups of 
Vehicles 

The pressure level for an M3A1 tank oper¬ 
ated at a distance of 133 yd was observed to be 
81 db. If two tanks were operated at this same 
distance, the theoretical pressure level at the 
observation post would be 84 db or an increase 
of 3 db; with four tanks the pressure level 



NUMBER OF M3A1 TANKS 

Figure 11. Increase in the intensity at the ob¬ 
servation post due to the sound of N vehicles, 
arranged as shown in sketch, over the intensity 
due to a single vehicle at 133 yd. Based on: 9 db 
loss per distance to vehicles doubled; 2.25 db gain 
per number of vehicles doubled. 


would be 87 or an increase of 6 db. Each time 
the number of tanks doubles, the intensity 
theoretically increases 3 db as shown in curve 
A, Figure 10. Curve B shows the theoretical 
maximum intensity at the observation post 
from a number of tanks spaced at 25 yd apart 
traveling in a line at right angles to the obser¬ 
vation post, the shortest distance from the op¬ 
erating post to the line being 133 yd. Owing to 
the fact that the tanks on either side of the 
nearest one are progressively more distant from 
the observation post, curve B shows a diminish¬ 
ing rate of increase of intensity as the number 
of tanks increases. 

The assumed loss of intensity with increase in 
distance noted on Figure 10 is not the familiar 


inverse square law which corresponds to a 6- 
db loss per distance doubled, but an observed 
loss of 9 db per distance doubled. The exact 
value depends on the terrain, meteorological 
conditions, and frequency spectrum of the 
sound under observation. Curves C, D, E, and 
F of Figure 10 are plotted with a loss of 9 db 
per distance doubled, but with various assumed 
increases of intensity per number of vehicles 
doubled, as indicated on the respective curves. 

The curve in Figure 11 has been plotted to 
conform with an increase in intensity of 2.25 db 
per number of tanks doubled and 9 db decrease 
per distance doubled, and is therefore identical 
with curve D of Figure 10. This curve shows 
reasonable agreement with the points plotted 
from measurements. 


12.3.3 Principles of Masking 

To avoid destruction from gun fire, masking 
devices must of necessity be located at a dis¬ 
tance of several hundred yards from the enemy. 
The high frequencies of a complex sound are 
attenuated more rapidly than the low frequen¬ 
cies with distance. As a sound approaches 
threshold due to distance only the low frequen¬ 
cies remain. For this reason, and because the 
energy content of the sounds of vehicles is small 
in the high frequencies, the problem of masking 
Army vehicles at a distance becomes largely 
one of masking the low frequencies. 

One sound can mask another only when it is 
of greater intensity. The greater the difference 
in frequency between the two sounds, the more 
must the intensity of the masking sound exceed 
that of the masked sound. 

The nearer the pattern of the masking sound 
approaches that of the sound to be masked, the 
more difficult it is to detect the latter. For these 
reasons it is desirable that a masking sound be 
similar in pattern to the sound masked and 
equal or lower in frequency. If the noise to be 
masked is not steady but, like the sound of 
motors and vehicles, has a fairly regular and 
characteristic temporal sequence or pattern, 
imitating the temporal pattern as well as the 
frequency pattern by the masking sound makes 
it more effective as a masker. 





















128 


SOUND SIMULATION AND MASKING 


12 3 4 BTL Siren 

The BTL siren used in the work differs from 
that described in reference 2 in that it is 
equipped with a horn designed for a theoretical 
cutoff frequency of 75 c. It develops a sound in- 



Figure 12. Oscillogram of BTL siren. One cycle 
of a repeating wave. Fundamental frequency: 
470 c; azimuth: 0 degree; distance: 1,000 ft. 


tensity of 133 db at 100 ft. The fundamental 
frequency can be varied between 60 and 500 c. 
The siren consists of an air compressor, a com¬ 
pressed air chamber fitted with six port holes 



Figure 13. Oscillogram of BTL siren. One cycle 
of a repeating wave. Fundamental frequency: 

230 c; azimuth: 0 degree; distance: 1,000 ft. 

arranged in a circle, a chopper consisting of a 
disk with six extensions each of which covers a 
respective port, means for rotating the chopper 
to open and close the ports, and a multiple horn 



Figure 14. Oscillogram of BTL siren. One cycle 
of a repeating wave. Fundamental frequency: 

115 c; azimuth: 0 degree; distance: 1,000 ft. 

into which the ports exhaust. The fundamental 
frequency is determined by the speed of the 
chopper. 


Figures 12, 13, and 14 are oscillograms of the 
wave form of the siren at chopper speeds of 
4,700, 2,300, and 1,150 rpm respectively, corre¬ 
sponding to fundamental sound frequencies of 



Figure 15. Oscillogram of single Canary motor. 
One cycle of a repeating wave. Fundamental fre¬ 
quency: 71 c; azimuth: 0 degree; distance: 1,000 
ft. 

470, 230, and 115 c. The tracings as shown in 
Figures 12 and 14 cover less than a complete 
cycle. 

The siren is well adapted to mask the sound 
of Army vehicles because of its great intensity 



Figure 16. Oscillogram of single Canary motor. 
One cycle of a repeating wave. Fundamental fre¬ 
quency: 60 c; azimuth: 0 degree; distance: 1,000 
ft. 

and the fact that its harmonic content is reason¬ 
ably similar to that of Army vehicles. Its vari¬ 
able fundamental frequency allows for adjust¬ 
ment to an optimum frequency for masking a 
given sound. 



Figure 17. Oscillogram of single Canary motor. 
One cycle of a repeating wave. Fundamental fre¬ 
quency: 33 c; azimuth: 0 degree; distance: 1,000 
ft. 

1235 Canary 

The construction and performance of the 
Canary have been described in Section 12.2. It 


CONFIDENTIAL V 










129 


MASKING THE SOUNDS OF MILITARY VEHICLES 


produces a sound intensity of 123 db at 100 ft. 
Wave forms of a single Canary motor at speeds 
of 71, 60, and 33 c are shown in Figures 15, 16, 
and 17. By operating the two motors at slightly 
different speeds, beat notes of almost any de¬ 
sired low frequency are developed. 

The Canary is suitable as a masking device, 
not only because it has a fairly high intensity, 
but also because it has a sound pattern resem¬ 
bling that of motor vehicles. For this reason, it 
requires a smaller intensity differential to mask 
vehicle sounds than is required of dissimilar 
sounds. 


12.3.6 Observations and Conclusions 

Over 200 determinations were made of the 
distance (over flat, grassy terrain) at which 
the sounds of Army vehicles (M4A3 tanks, 
M3A1, and 21 / 2 -ton trucks) were masked by 
either a BTL siren or a Stevens Institute 
Canary. 

Both devices proved to be very effective as 
maskers and about equivalent to one another. 
Either one can mask the sound of a formation of 
17 MU AS tanks moving in normal formation if 
it is as close to the enemy outpost as the nearest 
tank. If more maskers are used, they may be 
placed at greater distances from the enemy. 
For example, 17 M4A3 tanks in a column ap¬ 
proaching an observation post can be masked 
with reasonable certainty to within 700 yd of 
the post by the following combinations: 


Number of 
maskers 
8 
6 
4 
2 
1 


Distance of 
maskers 
1,220 yd 
1,135 yd 
1,005 yd 
830 yd 
700 yd 


Trucks are easier to mask than tanks. A 
Canary a mile away can on the average mask 
two 2Y2-ton trucks to within 150 yd of an obser¬ 
vation post. The Canary is slightly more effec¬ 
tive than the siren for masking trucks. 

The distance at which vehicles may be suc¬ 
cessfully masked is directly proportional to the 
distance of the masker. The ratio does not 
change significantly as the distance of the 


masker is increased, except that at some outer 
limit (approximately 2 miles) the intensity of 
the masker is so low that it may fail completely 
to mask the vehicles, its influence being small 
compared with that of the background noises. 
At this distance, also, transmission variations 
due to variations in meteorological conditions 
are so great as to render specific conclusions im¬ 
possible. 

The distance at which masking of a given 
pair of vehicles occurs on repeated trials with a 
masker at constant distance varies from about 
half to about double the median distance. The 
chief cause of the variations is fluctuation of the 
velocity and direction of the wind. An adequate 
study of the relation between effectiveness of 
masking and meteorological conditions would 
require an estimated 2,000 observations in the 
field. Such a study should be made and should 
be extended to cover several varieties of ter¬ 
rain and a wider range of wind velocity. Almost 
all the present study covers only grassy terrain 
and the moderate winds of fair spring and sum¬ 
mer weather at Pine Camp, New York. 

The theoretical principles have been derived, 
and are supported by preliminary experiments, 
for calculating the number and distances of 
maskers required to mask any number of ve¬ 
hicles traveling in their usual formations to 
within any specified distance of the enemy. The 
accuracy of such predictions and the allowance 
that must be made to insure against failure due 
to momentary variations of acoustic transmis¬ 
sion are both improved by taking into account 
the expected wind and temperature conditions. 
The method of solution of a typical problem is 
illustrated in reference Id, and it is pointed 
out that tables and graphs can be constructed 
which would make it quite simple to determine 
the number and position of masking devices re¬ 
quired to mask the sounds of the movement of 
any group of Army vehicles. It is also shown, 
however, that, owing to the vagaries of sound 
transmission over considerable distances, it is 
impossible to insure continuous masking with 
absolute certainty without profligate use of 
maskers at short range. It is possible, however, 
to calculate a more reasonable use of maskers 
that will insure masking to various degrees of 
certainty, such as 50 per cent, 80 per cent, or 





130 


SOUND SIMULATION AND MASKING 


95 per cent. Several psychological factors, such 
as the uncertainty of enemy observers as to the 
time at which to listen most carefully for the 
sounds of the vehicles and their uncertainty as 


to just what kind of sound to listen for, will un¬ 
doubtedly tend to make masking more success¬ 
ful than it was under the experimental condi¬ 
tions. 


AL 





Chapter 13 

MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


13 1 SOUND TRANSMISSION AND 
RECEPTION 

T he sound level received at the enemy’s po¬ 
sition is of vital importance to successful de¬ 
ception. If the sound is too loud, there is greatly 
increased possibility that it will be recognized 
as a recording, while, if it is too low, it will not 
be heard at all. No quantitative data were avail¬ 
able on the best deceptive level or upon the 
transmission loss that must be anticipated be¬ 
tween a sound source and a distant listening po¬ 
sition. An investigation was therefore under¬ 
taken to supply such data for transmission over 
land, the work being done at the Army Experi¬ 
mental Station [AES], Sandy Hook, between 
September 1, 1943 and January 31, 1944, as a 
part of Project 17.3-4.1. 1 

The principal factors to be investigated 
were: 

1. The intensity and character of the sound 
at the source; 

2. The transmission loss between the source 
and the listening position; and 

3. The masking noise at the listening position. 
The first of these is controlled by the fre¬ 
quency spectrum of the particular sound being 
used and by the characteristics of the repro¬ 
ducing equipment. The transmission loss is a 
complex function of frequency, distance, atmos¬ 
pheric conditions, and type of terrain. The 
masking noise varies widely from time to time. 
It does, however, have a reasonably stable mini¬ 
mum value which happens to be of particular 
interest in sound deception. 


1311 Sound Source 

Sound Recordings 

The solution of technical problems associated 
with the recording program constituted a sub¬ 
stantial part of the assistance rendered to the 
Army Experimental Station under NDRC aus¬ 
pices. 

The possibility of using recordings obtained 


from commercial sound libraries (motion pic¬ 
ture and broadcast sound effects) was consid¬ 
ered, but such recordings do not offer an ade¬ 
quate variety of sounds. Trained observers can 
recognize, with varying degrees of certainty, 
not only vehicle types (particularly tanks) but 
whether vehicles are ascending or descending a 
hill, whether they are head on or broadside, 
and whether their engines are idling or driving 
the vehicles at slow speed. It is, therefore, essen¬ 
tial that sounds be recorded in all their varia¬ 
tions for all important types of military ve¬ 
hicles. 

Practically all commercial recordings of ve¬ 
hicle sounds are recorded close up. Pronounced 
doppler effects characterize sounds recorded in 
this way. Their use in an attempt to create an 
illusion a mile away is obviously ineffective. 

In making original recordings for sonic de¬ 
ception, new techniques were developed. One 
example consists of locating the microphone 
pickup at the center of a circle of continuously 
moving vehicles. In this way, the collective 
sound of motor vehicles of the required type and 
number is obtained continuously and at high 
level, free of the revealing doppler effect. 

Another technique is the exaggeration of in¬ 
cidental telltale sounds, such as the squeak of 
tank caterpillar treads. It is known that an ob¬ 
server strains to recognize these sounds. These 
can be accentuated by superposing them on an 
otherwise ordinary sound. 

The recording work was done both at Fort 
Hancock and Pine Camp, New York, a specially 
equipped truck and trailer being used for this 
purpose. The recorded material covers a large 
variety of military vehicles including tanks, 
and many other sounds of military interest, 
such as bridge building and field construction 
work. 

When a sound record is dubbed on a magnetic 
recorder and played back through an amplifier 
and loudspeaker, the frequency spectrum of the 
radiated sound will differ from that of the 
original record by the addition of the frequency 
characteristics of the magnetic recorder and of 


131 


132 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


the reproducing equipment. However, the dif¬ 
ferences between the spectra of the original and 
the reproduced sounds lose some of their sig¬ 
nificance under practical conditions of use, as 
will be illustrated later. 


131,2 Sound Transmission 

Meteorological Conditions 

The weather has a great influence on sound 
transmission, and a knowledge of local atmos¬ 
pheric conditions is necessary for either an 
analysis of sound level data or for the anticipa¬ 
tion of transmission loss that may prevail at 
some particular time. The detailed information 



TIME OF DAY 


Figure 1. Temperature gradient, elevation 5 to 
35 ft. 

needed is the humidity, the wind velocity and 
direction, and the vertical gradients of wind 
velocity and of temperature. The horizontal 
gradients and the temperature may be neglected 
since they have no important effect on trans¬ 
mission. The wind velocity gradient is defined 



Figure 2. Temperature gradient, elevation 35 to 
95 ft. 


as the change in velocity with elevation. It is 
measured in meters per second per meter and 
is almost always positive, i.e., the velocity in¬ 
creases with elevation. The temperature gradi¬ 
ent is the rate of change of temperature with 
elevation and is measured in degrees centigrade 
per meter. It may be either positive or negative, 


a positive gradient indicating an increase in 
temperature with height. 

A rather extensive series of meteorological 
measurements were made at Sandy Hook. Read¬ 
ings were made at elevations of 5, 35, 65, and 
95 ft. The temperature and velocity gradients 
were computed. Check measurements showed 
that the temperature conditions were stable 


a. 



Figure 3. Wind gradient, elevation 5 to 35 ft. 


over wide areas but that the wind conditions 
were not. Portable equipment was obtained and 
wind measurements made at each listening 
point simultaneously with the sound measure¬ 
ment. These supplementary data were confined 
to elevations of 5 ft and 15 ft. The data obtained 
at the time of sound measurements were useful 



Figure 4. Wind gradient, elevation 35 to 95 ft. 


in the analysis of those measurements but were 
not adequate for predicting future conditions. 

Average hourly temperature gradients be¬ 
tween elevations of 5 ft and 35 ft, and of 35 
ft and 95 ft are shown in Figures 1 and 2. The 
outstanding feature of the curves is that the 
gradients become negative at sunrise and re¬ 
main negative until sunset, both the 5 to 35 and 
35 to 95 gradients reaching a value of about 
—0.030 C per m in the middle of the day. At 
night, the average gradient is positive (about 
+0.010) near the ground but is zero in the 35- 
to 95-ft region. Individual readings vary widely 


<• ' I " > 






























































































SOUND TRANSMISSION AND RECEPTION 


133 


from the average, a range of +0.70 to —1.00 
having been recorded during the daytime. 

Similar curves of wind gradients are shown 
in Figures 3 and 4. The average values range 
from 0.20 to 0.50 m per sec per m near the 
ground and from 0.10 to 0.40 m per sec per m in 
the 35- to 95-ft region. The gradients are lower 
during the day than at night, but the sun has 
not nearly as pronounced an effect on the wind 
as on the temperature. The individual readings 
again varied greatly as is evidenced by the scat¬ 
tering of the average values. A range of —0.10 
to +1.00 m per sec per m was recorded. 

Since gradients are small differences between 
large numbers and require precision instru¬ 
ments for their accurate measurement, it would 
be convenient to correlate them with some more 
easily measured quantity. The relation of wind 
gradient to wind velocity was, therefore, deter¬ 
mined for this group of data. The curve of the 
average values follows the equation: 

w = 0.017TF 1 - 5 , 

where w is the wind gradient and W the wind 
velocity. Limit curves (Figure 5) are drawn to 
include most of the individual values. In gen¬ 
eral, the gradient at Sandy Hook may be ex¬ 
pected to be within ±0.20 of the value given by 
the equation. 

Physical Characteristics of 
Sound Propagation 

A sound wave traveling through the air to¬ 
ward a distant point will arrive with a greatly 
reduced intensity. The loss is due principally to 
four causes: dispersion, refraction, absorption 
by the air, and absorption by the surface over 
which the sound may be traveling. 

The dispersion loss is due to the sound wave 
having a constantly expanding spherical wave 
front. Its energy must, therefore, be distributed 
over an increasingly large area as it progresses, 
and the energy per unit area (intensity) is cor¬ 
respondingly reduced. This dispersion loss be¬ 
tween two points distant D x and D, from the 
source is 

Li = Loss in db = 20 log 

It amounts to 6 db every time the distance is 
doubled. 


In a homogeneous medium the sound rays 
travel in straight lines radiating from the 
source, but in a nonhomogeneous medium 
these rays will be bent by refraction. This is of 
interest in the present problem because most 
of the energy from a large loudspeaker is con¬ 
fined to a narrow cone and refraction may pre¬ 
vent centering this sound cone on the enemy’s 
position. 

The temperature gradient is one source of re¬ 
fraction because the velocity of sound is a func¬ 
tion of the temperature and a change of tem¬ 
perature with elevation will cause different 
parts of the sound wave to travel with different 
speeds. If the temperature gradient is positive, 










/ 

/ 









/ 

/ 








LIMI 

: 

it/' 

/ 


7 







/ AVER/ 

/ 






/ 

/ 



✓ 

S 




, / 

—+ 

/ 


r LI 

MIT 

7 " 





/ 

X 








* 


[± 

Y 

\ _ 


• 



1 




*6 e 10 12 14 16 18 20> 

VELOCITY METERS/SEC 


10 15 20 25 30 35 40 

miles/hour 

Figure 5. Wind gradient versus wind velocity. 


the portion of the wave front near the ground 
will be cooler and, therefore, will travel more 
slowly than the upper portion. This will cause 
the rays to be curved downward. Conversely, if 
the gradient is negative, the rays will be bent 
upward. 

A similar bending is caused by the wind ve¬ 
locity gradient. This is because the sound wave 
velocity is the vectorial sum of sound and wind 
velocities. A following wind will thus increase 
the wave velocity, and an opposing wind will de¬ 
crease it. This, by itself, would not bend the 
sound rays, but the wind velocity is always less 
near the ground than at higher elevations (posi¬ 
tive gradient), making the wind effects less pro¬ 
nounced on the lower portion of the wave. This 
results in the rays being bent downward by a 

































134 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


following wind and upward by an opposing 
wind. 

The wind factor is usually considerably 
greater than the temperature factor. For ex¬ 
ample, a tail wind of 2 miles per hour will 
almost neutralize the normal midday tempera¬ 
ture gradient of —0.025 C per m. 

The paths of refracted sound waves are 
shown diagrammatically in Figures 6 and 7. In 



Figure 6. Refraction effects with negative curv¬ 
ature. 


Figure 6 waves with negative curvatures are 
illustrated. Under this condition, the sound lit¬ 
erally bounces along the ground as it travels 
from source to listening point. Figure 7 illus¬ 
trates positive curvature. Here the sound 
curves upward so that beyond a certain point, 
designated A, the simplified theory indicates 
that it is impossible to transmit sound from the 
source to a listening point at the ground level. 
However, refraction is always accompanied by 
some reflection, and also, under practical condi¬ 
tions, there are always eddy currents and other 


/ * 4 


V 


DF=^r 


7 777777777777777777777777777 


Figure 7. Refraction effects with positive curva¬ 
ture. 


discontinuities in the air that tend to scatter 
the sound ray. This reflected and scattered 
sound energy will cover a large area and 
some of it will reach listening points beyond A. 
An eddy with attendant secondary sound rays 
is illustrated at B. It is readily apparent that 
transmission under these conditions will be 
greatly inferior to that when a negative curva¬ 
ture prevails. 

Absorption in air, the third factor in trans¬ 
mission loss, causes a reduction in sound inten¬ 


sity by converting sound energy into heat. It is 
a function of relative humidity, temperature, 
frequency, and distance. As humidity is an im¬ 
portant variable, it is convenient to refer to this 
as humidity loss. The change in intensity, 
caused by this absorption, is expressed by the 
equation 

I„ = he-^' a , 

where I 0 is the intensity at the source, I d is the 
intensity at distance d feet from the source, and 
m is an absorption coefficient. This equation 
may be changed to the form 

L 2 — 4.34md, 

where L 2 is the humidity loss in db. This equa¬ 
tion shows that this loss varies directly with 
distance. At frequencies below 1,000 c, the loss 
is less than 2 db per 1,000 ft, but at high fre- 



Figure 8. Transmission loss, range A, 1,000 c. 

quencies it becomes very large, reaching 18 db 
per 1,000 ft at 5,000 c and 30 per cent humidity. 

The final component of transmission loss is 
due to absorption by vegetation through which 
the sound must pass and by the surface over 
which it must travel. These losses must be de¬ 
termined empirically. 

In addition to the general effects considered 
above, the sound intensity will be influenced by 
local conditions. Buildings and steep hills 
closely in front of the source will cause large 
reflection losses, and a listening post sheltered 
by such things will have lower than normal 
sound level. Obstructions in the middle portion 
of the sound path will have a less pronounced 


FIDENT1 










































SOUND TRANSMISSION AND RECEPTION 


135 


effect. The loss in intensity will be more severe 
with positive curvature than with negative, for 
in the latter case the sound tends to ride over 
the obstruction and return to the ground beyond 
it. In general, obstructions are not a serious 
factor since the location of the sound source 
may usually be chosen to provide a clear sound 
field for a considerable distance and since an 
observation post will not normally be placed 
behind an obstruction. 


SOURCE 



Figure 9. Component factors in transmission 
loss. 


Experiments in Sound 
Transmission 

The transmission of sound was studied over 
three types of terrain: 

1. A flat sandy beach; 

2. Flat and densely wooded; and 

3. Also densely wooded but not so flat. 

Two S2M amplifiers and loudspeakers (see 
Section 13.2.2) broadcast a warbled tone of 
200-c band width generated by a Western Elec¬ 
tric Co. 113-A oscillator. Measurements of 
sound intensity were made at various distances 
up to 3,500 ft by means of a Western Electric 
Co. 630-A microphone and an Electrical Re¬ 
search Products, Inc. [ERPI] RA277 sound 
frequency analyzer. Satisfactory data were ob¬ 
tained for frequencies from 600 to 5,000 c. 

The sound intensity at distances of 1,000 ft 
or more fluctuated widely. The fluctuation in¬ 


creased with distance and with the turbulence 
of the air and amounted to as much as 30 db 
at 1,000 ft on gusty days. The sound levels that 
were recorded were based on the frequently 
recurring peaks of intensity because of the im¬ 
portance of the maximum sound level in tactical 
problems. 

Fifty-eight sets of sound transmission data 
were obtained under various combinations of 



Figure 10. Wind loss on barren terrain. 

wind direction and velocity. The temperature 
gradients were predominantly negative. A 
typical group of curves is shown in Figure 8. 

The transmission loss for any particular set 
of conditions is the summation of component 
losses due to dispersion, air absorption, surface 
absorption, and wind. The components are 
shown diagrammatically in Figure 9. 

The surface and wind losses are complex, and 
one of the main objectives of these experiments 



Figure 11. Wind loss on wooded terrain. 


was to evaluate them empirically. A factor inde¬ 
pendent of frequency in the residual loss was 
attributed to wind effect. With a following wind 
the effect was a gain of 3 db per 1,000 ft. 
Figures 10 and 11 summarize the wind losses 
determined on barren and on wooded terrain 
respectively. The wind effect was found to be 
greater over wooded terrain than on the open 


CONFIDEtJ^^^ 











































































136 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


beach, perhaps because of a stratum of high 
wind gradient at the level of the tree tops. 
Transmission proved to be erratic in the pres¬ 
ence of a cross wind and even more so during 
periods of dead calm. 

The surface loss for barren sandy terrain 
was found by subtracting the dispersion, 
humidity, and wind losses from the total loss. 
A factor dependent on frequency varied from 
0 to 4 db per 1,000 ft and was less at 1,000 c 
and greater for higher and also for lower fre¬ 
quencies. 

When the dispersion, humidity, wind, and 
surface losses indicated by the curves are added 
the sum agrees with the average measured 
transmission to within ±3 db. The trans¬ 
mission loss at any particular moment, how¬ 
ever, may depart from the average value by a 
considerably greater amount so that the ac¬ 
curacy of prediction is more nearly ±6 db. At 
other locations and over other terrains, the 
wind and surface losses will be different, and 
the error may be greater. More data, obtained 
under a wide variety of conditions, are neces¬ 
sary for satisfactory prediction of sound trans¬ 
mission over long distances, but it is believed 
that the present results are sufficiently accurate 
to permit the successful use of sound deception. 3 


13.1.4 Masking Noise and Reception 

Any frequency component of* a complex 
sound can be heard if the level of that com¬ 
ponent is above the masking level for that par¬ 
ticular frequency. As a result, conditions 
normally exist when a portion of a sound is 
clearly audible while other portions are masked. 
In predicting the reception of a sound it is, 
therefore, necessary to know the level and fre¬ 
quency spectrum of both the sound and the 
masking noise. 

The sound level is a function of the sound 
source and of the transmission loss, while the 
masking noise is controlled by conditions at the 
listening point. This noise will obviously vary 

a Many additional data under a wider variety of 
conditions were obtained subsequently at the Army Ex¬ 
perimental Station at Pine Camp. The results were 
incorporated in the ranging tables employed in actual 
combat operations. 


widely from time to time, but it will have a 
reasonably stable minimum value. This mini¬ 
mum will exist when natural noises, such as 
that of rustling leaves and of the wind blowing 
past the ears, are the only sounds of importance. 
This level is of particular interest in sound 
deception because a listening post will normally 
be located in a quiet spot and also because the 
most effective results are obtained when the 
sound effects are audible only during lulls in 
the local noises. 

The noise made by surf on a beach is also a 
stable natural noise. A very limited amount of 
data was obtained on its characteristics along 
the north New Jersey shore. It was found that 
the intensity levels 50 ft from the water edge 
were within the range of 70 to 90 db. On a 
gently sloping sandy beach, the intensity was 
quite steady, but on a steep or a rocky shore it 
was intermittent with variations of the order 
of 20 db. The frequency spectrum was found to 
be substantially flat below 500 c and to decrease 
10 to 12 db per octave above that frequency. 
The level decreases rapidly as the listening 
point is moved inland and locations can usually 
be found within 100 yd where the surf noise is 
less than wind noise. Surf noise, therefore, 
should normally be disregarded for tactical pur¬ 
poses as any attempt to ride over it would make 
the sound too loud inshore. 

Minimum Masking Noise 

The masking noise level and spectrum were 
determined by three methods. In the first 
method, single-frequency sounds were gen¬ 
erated by an S2M system and projected 4,000 ft. 
The sound level was first measured at full power 
as a reference, and the power of the source was 
then reduced until the sound was just audible. 
This latter sound level is equal to the masking 
noise and is found by subtracting the power 
reduction from the reference level. The fre¬ 
quency range covered was from 600 to 5,000 c. 
These data were then transformed to an equi¬ 
valent intensity-per-cycle basis for continuous 
sounds and plotted. 

The second method was the direct measure¬ 
ment of the noise with a 630-A microphone and 
an RA227 sound frequency analyzer. No wind 
screen was used on the microphone during the 


CONFIDENTIAL \ 







SOUND TRANSMISSION AND RECEPTION 


137 


test. Limitations of the equipment restricted 
the reading to low frequencies where the noise 
level is comparatively high. The average overall 
intensity levels are: 


Wind Velocity 
1-6 mph 
6-13 mph 
13-18 mph 


Intensity Level 
49 db 
56 db 
62 db 


The third method consisted of listening tests 
by a number of observers to determine the 
minimum level at which the insertion of a high- 
pass filter could be detected. The manner in 



FREQUENCY IN CYCLES PER SECOND 


Figure 12. High-pass filter test of sound recep¬ 
tion. 

which this served to locate the masking level is 
illustrated in Figure 12. If the sound is at level 
A in the figure, the introduction of a 200-c high- 
pass filter will be heard because the sound level 



Figure 13. Wind noise masking of continuous 
spectrum sounds. 

is higher than the noise level for an appreciable 
band below 200 c. If the sound level is decreased 
to B, the insertion of the filter will no longer be 
heard because all sound components below 200 
c were already masked by the noise. The level 
below which the filter could not be detected is, 
therefore, a measure of the masking noise at the 
filter cutoff frequency. 


These tests were made with an AES-4X sys¬ 
tem (see Section 10.2.3) as a source and with 
the listening position 100 ft from the horn. The 
range of tactical sounds was covered by using 
thermal, Model A Ford, and tank noises. The 
sound level was determined as in method 1 by 
measuring it at full power and then attenu¬ 
ating it the known amounts. The corresponding 
masking levels are plotted in Figure 13. This 
figure contains data from all three methods and 
smooth curves of masking noise levels as a 
function of frequency have been drawn for 
wind velocity ranges of 1 to 6, 6 to 13, and 13 
to 18 mph. A fourth curve representing abso¬ 
lutely quiet conditions was derived from the 
threshold of audibility. It is of only theoretical 
interest since some noise is always present. 
These curves may be used to determine the 
masking effect of wind noises upon any sound 
that has a reasonably continuous frequency 
spectrum. For this purpose, the sound spectrum 
must be plotted on an energy-per-cycle basis. 

These tests illustrate the difficulty of detect¬ 
ing the presence or absence of the very low 
frequency components of a sound. A corollary 
is that it is not necessary to reproduce those 
components. This is of value since raising the 
low-frequency cutoff of a system permits sub¬ 
stantial reductions in its size and weight. It 
appears that the low-frequency cutoff may be 
made at about 80 c since it is unlikely that a 
deceptive sound will reach the observer at a 
high enough level for lower-frequency com¬ 
ponents to be heard, even if they are present. 
Similar tests with low-pass filters showed that 
frequency components above 5,000 c could not 
be heard at distances exceeding a few hundred 
feet. This restriction of the effective frequency 
range to between 80 and 5,000 c is confirmed 
by the analyses of typical problems. These facts 
provided the justification for simplifying the 
AES-4X system before it was produced in 
quantity as the AES-4 (see Section 13.2.3). 

Sound Intensity Suitable for Deception 

The sound must have a level well above the 
masking noise for high quality reception. How¬ 
ever, as stated before, it appears best for decep¬ 
tive purposes to maintain the level close to the 
masking noise so that the observer can hear it 





























































i38 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


only during quiet periods in the local noise. 
During these quiet periods, it is necessary that 
the listener hear a sufficiently wide frequency 
band to give the sound character. It is found 
that for the great majority of sounds, this band 
is most effective when centered below 500 c. If 
the band is too narrow or at too high a fre¬ 
quency, all sounds tend to sound like escaping 
steam. Experience to date indicates that 
optimum conditions are obtained with a band 
width of at least two octaves having an intensity 
level about 15 db above the masking level. 

The sound technician must produce this level 
by controlling either the signal voltage at the 
loudspeaker, or the distance over which the 
sound is transmitted. Under field conditions, 
there is neither time nor personnel available to 
compute these values. Operating tables valid 
for practically all operating conditions have 
therefore been prepared listing the voltage and 
the maximum range for four types of systems 
(S2M, AES-1, AES-2, and AES-4). This re¬ 
duces field procedure to the simple operation 
of looking up a value in a book. 1 


sisting of an assembly of component parts that 
had been designed largely for other purposes. 
The other lot, known as the Junior Heaters 1 
and assigned Army Experimental Station 
[AES] numbers, have 250-watt power capacity 
and were developed specifically for this purpose. 
One S2M and ten AES systems were built under 
OSRD contract (Projects 17.3-4.2 and 17.3-4.3). 


13 - 2 - 2 Heater (S2M) 

The Heater consists of a magnetic recorder- 
reproducer, an amplifier, two loudspeakers, a 



132 SONIC DECEPTION: HEATERS 

i3.2.i Experimental Equipment 

Developed for the Armed Forces 

The acoustic equipment for sound deception 
consists, fundamentally, of a means of storing 
and reproducing sound effects, of amplifiers and 
loudspeakers, and of a power supply. The mag¬ 
netic type of recorder-reproducer was selected 
because it is capable of good fidelity and volume 
range, is compact and portable, and withstands 
shock and movement during use; and, further¬ 
more, the records do not require any processing. 
The essential feature of the amplifier and loud¬ 
speaker is that they have an adequate power 
capacity and fidelity to cover the tactical re¬ 
quirements. Either a battery or a gasoline 
engine generator may be used for supplying 
power. 

Two distinct classes of equipment were de¬ 
veloped. The first, known as the Heater 1 and 
later designated S2M and more recently Heater 
Mark 1 by the Navy, is a 500-watt system con- 


Figure 14. Component parts of Heater. 

battery, a rotary converter, and necessary spare 
parts and accessories. All units except the loud¬ 
speakers are housed in portable weatherproof 
wooden boxes. Flexible cables with waterproof 
plugs and jacks are used to interconnect the 
various units. An assembled system is shown in 
Figure 14, and its schematic circuit diagram in 
Figure 15. The dimensions and weights of the 
units are listed in Table 1. 


Table 1. Dimensions and weights of Heater 
(Western Electric Code No. X-66021). 


Unit 

Length 

(in.) 

Height 

(in.) 

Width 

(in.) 

Weight 

(lb) 

Battery- 

32 

18 

17 

280 

Converter 

32 

22 

21 

300 

Reproducer 

25 

21 

16 

90 

Amplifier 

24 

47 

24 

415 

Loudspeaker A 

29 

17 

22 

240 

Loudspeaker B 

29 

17 

22 

240 

Accessories box 

36 

14 

24 

175 

Total 




1,740 


CONFIDENTIAL * 













SONIC DECEPTION: HEATERS 


139 


The magnetic recorder-reproducer is a stand¬ 
ard design manufactured by the Armour Re¬ 
search Foundation. The recording medium is 
0.004-in. music wire, about two miles of wire 
being required for a 30-minute recording. Lon¬ 
gitudinal magnetization with high-frequency 
bias and erasure is used. The wire is driven 
from one spool to another by an induction motor 
through friction clutches and belts, and must be 
rewound before a record is reproduced. 

A preliminary and a power amplifier are 
housed in one box. They are Western Electric 
products designated D-150300 and D-150229 


plastic throat assemblies. Rectangular horns 
having a conical flare are used, the mouth of 
each horn being 7.25 in. by 9.5 in. These horns 
are assembled together in a 3 by 2 pattern so 
that the mouth of the assembly is 14.5 in. by 
28.5 in. A plywood horn extension is provided 
to increase the size of this opening to 20 in. by 
40 in., and normally the two loudspeakers of 
the system are mounted side by side to form a 
square. 

The battery was designed originally for use 
in torpedoes. It is of the lead storage type with 
24 cells capable of delivering 35 amperes for 



and are used in general announcing systems 
aboard ships of the U. S. Navy. The power 
amplifier consists of a single class B stage and 
is capable of delivering 500 watts to a 20-ohm 
load. Forced ventilation is provided. 

The loudspeakers were also designed for the 
Navy’s general announcing systems. Each 
speaker, designated Western Electric Co. 
D-173234, consists of an assembly of six re¬ 
ceiver units and six horns. The receivers are 
of the moving coil type and have permanent 
magnet fields. The diaphragms are of phenolic 
impregnated fabric, and the coils are wound 
with enameled copper wire. Their resonant fre¬ 
quency is about 550 c. The diaphragms are 
acoustically coupled to the horns by molded 


30 minutes at a nominal 48 volts. It is designed 
for short life but may be used for a number of 
duty cycles if recharged promptly. A thermo¬ 
statically controlled heater is provided. 

A rotary inverted converter is also provided. 
It is driven by the battery and has an a-c ca¬ 
pacity of 2 kva at 115 volts, 60 c, 3-phase, with 
a 90 per cent power factor. The 3-phase power 
is required by the amplifier which was designed 
for use on warships having this supply. Its 
speed is 1,200 rpm. This unit will supply suffi¬ 
cient power to operate the reproducer and the 
amplifiers. 

The converter may be started and stopped 
by a manual switch on the control panel, and 
the magnetic reproducer may be controlled by 


riAL 




















































































140 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


a switch on its panel. In addition, a time switch 
is provided to start the converter automatically 
at any selected time within 24 hours. Circuits 
are also provided so that the apparatus may be 
started and stopped by remote control and so 
that the amplifier and loudspeakers may be used 
as the audio end of a radio receiver. In addi¬ 
tion, an auxiliary switch is closed when the 
magnetic recorder has reached the end of its 
program. This switch could be used to actuate 



200 3 4 5 6 8 1000 2 3 4 5 6 7 8 10000 

FREQUENCY IN CYCLES PER SECOND 


Figure 16. Frequency response of Heater. 

a detonator. Accessories consist of a micro¬ 
phone, operating cables, hydrometer syringe, 
tools, and spare parts such as vacuum tubes, 
fuzes, and plugs. 

Performance 

The frequency-response curves of the mag¬ 
netic reproducer, the amplifiers, and the loud¬ 
speakers are shown in Figure 16. The restricted 
low-frequency response of the loudspeakers to¬ 
gether with their high efficiency in the 1,500-c 
region provide excellent transmission of speech 
in noisy areas. The low-frequency cutoff is pri¬ 
marily due to the stiffness of the diaphragm 
assembly. Such characteristics, in general, 
limit the use of this equipment in deceptive 
work to suggestive caricature of typical sounds 
rather than faithful reproduction. This speaker 
was used because it was more powerful than 
any other. 

As the loudspeaker will not reproduce the 
lower-frequency components of a sound, it 
would obviously be inefficient to waste amplifier 
capacity on them. The frequency response of the 


amplifier is, therefore, cut off sharply below 
400 c. This is done in the preamplifier so that 
the full 500-watt capacity of the power amplifier 
is available for the higher frequencies. 

The overall capabilities of the system are 
shown in Figure 17 where the sound intensity 
on the horn axis 30 ft from the mouth is plotted 
as a function of frequency. The data were ob¬ 
tained with the two loudspeakers located side 
by side (the manner in which they were ulti¬ 
mately used). Single-frequency tones were used. 
The volume controls were adjusted so that at 
1,000 c the amplifier delivered 500 watts to the 
loudspeakers. The intensities shown in Figure 
17 are the maximum available. A signal-to- 
noise ratio of 30 to 35 db, imposed by the mag¬ 
netic reproducer, was the best that was avail¬ 
able in this system. 

In general, the S2M systems have proven val¬ 
uable in the field and are still the most powerful 
ones available. 



Figure 17. Sound intensity level of Heater. 


1323 Junior Heater (AES) 

Experience with the Heater and initial work 
at the Army Experimental Station indicated 
the need for a system that covered a wider 
frequency range, that was more readily porta¬ 
ble, and that included a more rugged magnetic 
reproducer. In order to limit the weight and 
bulk, the power capacity was limited to 250 
watts, half that of the Heater. Nearly all of the 
component units had to be designed specifically 
for this purpose. A typical system consists of 
an alternator driven by a gasoline engine, a 
magnetic recorder-reproducer, an amplifier, 


v FTDENTIAL 
















































































SONIC DECEPTION: HEATERS 


141 



TWO BY TWO 
LOUDSPEAKER UNIT 


AMPLIFIER 
UNIT 


GASOLINE ENGINE 
DRIVEN ALTERNATOR 


TWO BY TWO 
LOUDSPEAKER UNIT 


Figure 18. 


Component parts of Junior Heater (AES-1). 



Figure 19. Simplified schematic circuit of Junior Heater 










































































































































142 MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 



Figure 20. Circuit of recorder-reproducer (Junior Heater) 





































































































































































































































































SONIC DECEPTION: HEATERS 


143 


two loudspeakers, an accessories box, a maga¬ 
zine box containing spare magazines for the 
magnetic recorder, tripods for mounting the 
loudspeakers, and mounting details for install¬ 
ing the system in a jeep. A depot spares box is 
supplied with each group of systems. Input con¬ 
nections are provided so that either a magnetic 
microphone (D-173334) or a carbon lip micro¬ 
phone (D-173335) may be used in place of the 
magnetic reproducer to convert the equipment 
to a public address system. The loudspeakers 
can be a pair of any one of three types desig¬ 
nated AES-1, AES-3, and AES-4, and the sys¬ 
tems are commonly referred to by the loud¬ 
speaker type. Thus a Junior Heater equipped 
with AES-1 speakers is known as an AES-1 
system. The units of a system are connected to 
each other by flexible cables with a weather¬ 
proof plug on each end. An AES-1 system is 
shown assembled for transportation in Figure 
18, and a simplified circuit diagram is shown in 
Figure 19. The size and weight of each of the 
component parts are given in Table 2. 

Magnetic Recorder-Reproducer 

The improved magnetic recorder-reproducer 
used with this equipment was developed jointly 
by the Bell Telephone Laboratories and the 
Brush Development Company under a Navy 
contract. It is designated the KS-12009 mag- 


Table 2. Dimensions and weights of Junior 
Heater. 


Unit 

Length 

(in.) 

Height 

(in.) 

Width 

(in.) 

Weight 

(lb) 

Engine alternator 

25 

18 

18 

125 

Reproducer 

25 

22 

15 

140 

Amplifier 

22 

17 

15 

150 

*Loudspeaker AES-1 

24 

19 

17 

56 

AES-3 

43 

25 

25 

45 

AES-4 

35 

48 

24 

125 

fTripod 

38 

6 

6 

21 

Accessories box 

22 

11 

15 

60 

Magazine box 

16 

13 

9 

50 

Cable bag 

10 

20 

20 

25 

Depot spares box 

36 

15 

26 

160 


* Two loudspeakers of one type required, 
t Tripods not used with AES-4. 


netic recorder and is manufactured by the 
Brush Company. Its schematic circuit diagram 
is shown in Figure 20. The recorder consists 
of two parts, an amplifier case permanently 


assembled in the box and a removable maga¬ 
zine. The amplifier case contains an amplifier, 
an oscillator, a motor, manual switching and 
control circuits, and input and output recepta¬ 
cles. The magazine contains all moving parts 
except the motor; these include the magnetic 
wire, the recording-reproducing head, an erase 
coil, timing indicators, and automatic control 
switches. The magazine is easily removable 
from the amplifier case, connections being made 
through plugs and jacks in the electric circuits 
and a spline coupling on the motor shaft. When 
the magazine is mounted in one position, the 
motor couples directly to one of the wire spools, 
and the wire can be pulled in the forward di¬ 
rection. If the magazine is rotated 180 degrees, 
the motor will couple to the other spool, and the 
wire can be rewound. Figure 21 is a view of 
the magazine with cover removed. A magazine 
will provide a half-hour reproduction, and a 
continuous program of indefinite length may 
be obtained by using two amplifier cases and a 
number of magazines or by using only one am¬ 
plifier case if interruptions of a few seconds 
while changing magazines can be tolerated. 

The recording is made by longitudinal mag¬ 
netization of 0.006-in. stainless-steel wire mov¬ 
ing at about 5 ft per sec. Linearity is obtained 
by the use of a 20-kc bias current superimposed 
on the recording signal current. The same elec¬ 
tromagnetic structure is used for reproducing 
and for recording. 

The timing mechanism is in the magazine 
and is controlled by the movement of the wire. 
It indicates minutes and seconds of recording 
time from the start of the wire. Limit switches 
associated with it stop the motor just before the 
end of the wire in both the forward and the re¬ 
verse directions. 

The recording efficiency of the wire and head 
is greatest at about 1,500 c and decreases sub¬ 
stantially at both higher and lower frequencies. 
Equalizers are provided to compensate for this, 
and the resulting overall frequency character¬ 
istic is approximately flat from 200 to 5,000 c. 
The volume range is about 40 db. 

Microphones 

A magnetic or a carbon microphone may also 
be used for the input signal for the amplifier. 


XFIDENT 










144 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


In the field of deception, this is of little value, 
but the existence of this feature makes possible 
the rapid conversion of the equipment into a 
high-power public address system. 

Amplifier 

The amplifier unit includes the preliminary 
amplifier, power amplifier, filament and plate 
supply for both amplifiers, ventilating fan, and 
input networks. The equipment inside its box 
is protected from rain, dirt, and dust. The vol¬ 
ume control knob is located under an auxiliary 


application of high voltage to the plates of the 
rectifier tubes until the filaments are heated. 
The operation of the thermostatically operated 
relay closes the winding of the electromagnetic 
relay causing it to pull up and lock. The oper¬ 
ation of the electromagnetic relay closes the 
filament circuit of the power amplifier tubes 
and the plate circuit of the rectifier tubes, and 
opens the heater resistance circuit of the ther¬ 
mostatically operated tube. 

The amplifier has a maximum gain of 94 db 
and an output capacity of 250 watts into 4.5 



LEVEL Wl 
FEED REEL 


'T_ .. 

SECONDS DIAL- 1 


SE COIL 
INUTES INDEX 


-REPRODUCING & RECORDING 
TAKE UP REEL 


HEAD 


Figure 21. Magazine of recorder-producer (Junior Heater). 


weatherproof metal cover next to the inlet 
ventilating hood. By turning back the metal 
cover, the weatherproof volume control knob 
is exposed, and the electric eye may be viewed 
through a Lucite panel. The amplifier circuit 
is shown schematically in Figure 22. 

The preliminary amplifier consists of two 
resistance-coupled stages plus two resistance- 
coupled push-pull stages with transformer 
coupling between them. 

The power amplifier consists of a single push- 
pull stage transformer coupled to the prelim¬ 
inary amplifier and to the output, and includes 
a self-contained power pack. The power pack 
also provides the filament, plate, and screen 
currents to the preliminary amplifier. To avoid 
any danger of damaging the rectifier tubes of 
the power amplifier, a thermostatically operated 
time delay relay is provided which delays the 


ohms. The frequency characteristic is flat from 
50 to 10,000 c. 

Loudspeakers 

The series of loudspeakers differ from one 
another primarily in their size and construction 
and in their low-frequency cutoff, the AES-1 
having the highest cutoff and the AES-4 the 
lowest. The AES-1 and the AES-3 use the same 
receiver unit, the difference in their charac¬ 
teristics being controlled by their horns. The 
receiver is of the moving coil type with a per¬ 
manent magnet field. The coil is of enameled 
copper wire and the diaphragm of phenolic 
impregnated fabric. It has an impedance of 
9 ohms and a power capacity of about 30 watts. 

The AES-1 loudspeaker consists of four re¬ 
ceiver units mounted in the corners of a square 
and coupled to four 250-c exponential horns. It 

















































































































































































































































































































































SONIC DECEPTION: HEATERS 


145 


is shown in Figure 23. The units are connected 
in series-parallel so that the loudspeaker im¬ 
pedance is 9 ohms. The frequency response has 
rather sharp cutoffs at 350 and 6,000 c and a 
broad 10 db peak at about 2,000 c. The sound in¬ 
tensity on the axis 30 ft from the horn mouth, 





Figure 23. Loudspeaker AES-1. 

for an input of 125 watts single frequency, is 
shown in Figure 24. As the effective mouth di¬ 
mensions are only about 15 in. by 15 in., the 
sound is spread over a large angle. At 500 c, 
the sound level 30 degrees off the axis is only 
1 db less than maximum. 

The AES-3 loudspeaker (Figure 25) also has 
four receiver units, but they are all coupled to 
the throat of a single 113-c horn. The combina¬ 


tion, coupler and horn, is 42 in. long. The fre¬ 
quency response is slowly rising from 130 to 
500 c, is flat from 500 to 3,000 c, dips at 4,000 c, 
and then recovers to 5,500 c. The sound inten¬ 
sity for 125 watts input is plotted in Figure 26. 
The horn has a mouth diameter of 24 in. This 
makes the 500-c sound level 2 db below maxi¬ 
mum at 30 degrees off the axis. 

Another loudspeaker was designed for ex¬ 
perimental use at Fort Hancock. It is known 
as the AES-4X, and consists of two Western 
Electric Co. KS-12004 cone-type receivers, two 
Western Electric Co. 713A high-frequency re¬ 
ceivers, and an electric frequency-dividing net¬ 
work. The cone-type units radiate through a 
60-c exponential horn, and the high-frequency 
units are coupled to a 250-c horn with a 6-in. 
mouth. The housing and low-frequency horn 


| 130 
8 



Figure 24. Sound intensity level of one AES-1 
loudspeaker. 


are of wood. The assembly has an effective fre¬ 
quency range of 50 to 15,000 c, as shown by the 
dotted curve in Figure 27. 

Using this speaker and a number of high- 
and low-pass filters, the maximum effective fre¬ 
quency range was determined for various op¬ 
erating conditions. These tests showed that 
neither the very high nor the extreme low fre¬ 
quencies were required. The high-frequency 
receivers and electric networks were, therefore, 
eliminated and the horn shortened by changing 
its taper from 60 to 90 c. In this form the as¬ 
sembly is known as the AES-4 loudspeaker. It 
is shown in Figure 28. 

The receivers in AES-4 have permanent mag¬ 
net fields and moisture-resistant paper cones 
and have an impedance of 20 ohms each. The 
four receivers, however, will not reliably with- 
























































146 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


stand 250 watts, and in operation the amplifier 
output is limited to 150 watts. The sound in¬ 
tensity developed with this input is shown in 
Figure 27. The frequency response is gradually 
rising from 70 to 3,500 c and then falls at a 


supplied by a Homelite alternator driven by a 
gasoline engine. It is rated at 115 volts, 60 c, 
single phase, 1,500 watts at 90 per cent power 
factor. It is equipped with automatic speed and 
voltage regulators but must be started man¬ 
ually. 



Figure 25. Loudspeaker AES-3. 

somewhat steeper rate from 3,500 to 10,000 c. 
The two units, mounted together, form a mouth 
48 in. square and, as a result, are quite direc¬ 
tional, the 500-c sound intensity 30 degrees off 
the axis being down 16 db. 


Power Supply 

Sufficient power to operate two systems is 


§ 



FREQUENCY IN CYCLES PER SECONO 


Figure 26. Sound intensity level of one AES-3 
loudspeaker. 

13 3 A REMOTE CONTROL DEVICE 
FOR HEATERS 

The RC (remote control) 2 is a radio device 
designed as an accessory to the Heater. Since 
one of the functions of the Heater is to attract 
enemy attention and possibly draw fire, the de¬ 
sirability of controlling such equipment from a 
remote position is obvious. 



Figure 27. Sound intensity level of two AES- 
4X and two AES-4 loudspeakers. 


Operational and Design 
Requirements 

To operate the Heater it is necessary to: 

1. Turn on the power to the receiver and the 
audio system; 

2. Start the wire recorder; 


































































































A REMOTE CONTROL DEVICE FOR HEATERS 


147 


3. Stop the recorder and turn off the power; 

4. Destroy the Heater by detonation. 

In designing the RC, an effort was made to 
provide a simple, light, rugged device con¬ 
structed of standard parts and to make it adapt- 




Figure 28. Loudspeaker AES-4. 

able for use with standard Army or Navy trans¬ 
mitters and receivers. 

Control by Selective Tuning 

The possibility was considered of selecting a 
carrier frequency and four modulation frequen¬ 
cies, one for each circuit to be controlled. It 
would be possible to separate the signals by 
means of selective filters and thus operate four 
separate relays to perform the four required 
functions. This method was rejected, however, 


because of the greater simplicity and economy 
of the alternative method described below. 

Operation of Stepping Switch by 
Signal Pulses 

In this method a single carrier frequency and 
a single modulation frequency are utilized. The 
modulation signal is pulsed the desired number 
of times by means of a telephone dial. The car¬ 
rier wave of the MN transmitter, as modulated 
by the control signal, is broadcast and received 
remotely by the MN receiver. The MN receiver 
output is fed directly to the RC receiver section. 
Here it is filtered and its pulses utilized to con¬ 
trol a sensitive relay which in turn operates a 
conventional telephone stepping switch. 

Three models of the RC were built on this 
general plan. The first was based on a modula¬ 
tion frequency of 500 c. This frequency proved 
unsatisfactory, however, because of the tend¬ 
ency of the equipment to be operated by speech 
signals from other stations. The situation was 
improved somewhat by using a modulation fre¬ 
quency of 1,000 c, but the instrument tended to 
be sluggish and not entirely reliable in its op¬ 
eration. The sluggishness was found to be in¬ 
herent in the electronic circuits employed and 
in the pulsing relay and stepping switch. 

The first model will not be here described in 
detail since the second and third models based 
on a modulation frequency of 16,000 c proved 
far superior. 


13.3.2 RC Mo( J el N() 2 

A modulation frequency of 16,000 c was se¬ 
lected because: 

1. The signal is not likely to be detected by 
listening; 

2. The signal carries a very small percentage 
of voice energy; 

3. The lagging, found so troublesome at 1,000 
c, is greatly reduced; and 

4. Very efficient filters for this frequency can 
be provided easily. 

A Navy (type MN) frequency-modulated 
transmitter and receiver was employed. It is 
assumed that the telephone stepping switch and 
also delay circuits appropriate for use with tele- 


t . 











148 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


phone dials and stepping switches are familiar 
both in principle and in operation. Both devices 
are employed in the RC Model No. 2. 

An inductive-capacitive filter was placed be¬ 
fore a voltage limiter in the receiving section 
to attenuate subharmonic frequencies of the 
modulation frequency and to add selectivity to 
the system. 

The basic filter system on which the selectiv¬ 
ity of the system depends consists of a parallel 
T null circuit in a degenerative path around a 
high-gain amplifier. The parallel T null circuit 
consists of two T networks, each of which is an 
attenuator and a phase shifter. 

It was found advantageous to introduce a 
peak limiter in advance of the T-filter in order 
to keep the maximum noise level at the pulsing 
relay below that which would operate the relay. 
In Model No. 2 a cathode follower was inserted 
after each amplifier in the T-filter as an im¬ 
pedance-matching device. This matching was 
required because of the high amplification re¬ 
quired by the high selectivity of the filter 
system. 


13 3 3 RC Model No. 3 

Further simplification was achieved in Model 
3 by substituting an inductive-capacitive filter of 
high selectivity for the T-network filter. Under 
favorable signal conditions, that is, when the 
signal-to-noise ratio is sufficiently high and 
static interference not so great as to prevent 
transmission of satisfactory voice signals, 
Model 3 operates with a high degree of relia¬ 
bility. Under marginal or bad receiving condi¬ 
tions, however, Model 3 is inferior to Model 2. 

Neither Model 3 nor Model 2 utilizes the 
audio band of frequencies, and therefore the 
control circuits do not diminish the usefulness 
of the transmitter and receiver for the usual 
audio purposes. 

No special precautions were taken to prevent 
detection of signals by the enemy. Since not 
more than four numbers are likely to be dialed 
and usually one is sufficient, it is apparent that 
detection must be done in a matter of 1.5 seconds 
or less. Although this is not impossible, it hardly 
seems probable. 


The possibility of operation on false signals 
can be greatly reduced by reducing the sensi¬ 
tivity with the volume control. In case the device 
does not operate reliably at reduced sensitivity, 
the probability of correct operation may be 
increased by repeated dialing of the number 
desired. Experience in the Hoboken area, at 
Fort Hancock, and at Pine Camp indicated that 
the danger of spurious operation from false 
broadcast signals is practically nil. 

Both Models 2 and 3 are IV /2 in. long, 5 x /2 in. 
wide, 6 in. deep, and weigh 10 lb each. The 
devices will stand as much abuse as their com¬ 
ponent parts, all of which are standard tubes, 
accessories, relays, and stepping switches. 

A complete field manual describing the cir¬ 
cuits employed, their adjustment and operation 
for both Models 2 and 3 has been prepared. 2 


13 4 THE WATER HEATER 

13-41 Introduction 

The Water Heater is a special naval mine 
that contains a high-powered acoustic system 
and timing devices for the projection of sound 
for deceptive purposes or for “psychological 
warfare.” The acoustic and timing systems 3 
were developed by the Bell Telephone Labora¬ 
tories, and the vehicle and power supply 4 were 
provided by the General Electric Company. The 
details of the division were established by 
agreement between the engineers of the two 
companies. 

General Description of the Water Heater 

The Water Heater is 21 in. in diameter by 
21 ft long and has the same physical contour 
as the Mark 18 torpedo. It is fired from a stand¬ 
ard submerged torpedo tube and runs for a 
predetermined distance along a preset course. 
Upon completion of its run, it drops anchor and 
rises to the surface, floating with its axis ver¬ 
tical and with the shell projecting about 2 ft 
out of the water. 

At a predetermined time, a loudspeaker is 
elevated 6 ft above the water and is pointed in 
a preset magnetic compass direction. A recorded 
sound program is then reproduced. The pro- 




THE WATER HEATER 


149 


gram may consist of speech or of tactical sounds 
such as engines, winches, and anchor chains. 
A total of 30 minutes of sound is available, and 
this may be broken into several intervals dis- 



Figure 29. Acoustic and timing system. 


tributed over 2 hours. The Water Heater may 
be set to arm or destroy itself at the completion 
of the program. 

The capabilities of the device are: 


Range 

Speed 

Running depth 
Angle fire 
Anchor cable 

Elapsed time between final 
adjustment and start of 
sound program 
Total duration of program 
Total duration of sound, di¬ 
visible into one to ten sepa¬ 
rate periods 

Sound range, adverse weather 
favorable 

Spread of effective sound beam 


5,000 yd max 
10 knots 
20-50 ft 

90 degrees right or left 
300, 600, or 900 ft 


12 hours max 
2 hours max 


30 minutes max 
1,000 yd 
6,000 yd 
60 degrees (30 
degrees from axis) 


Three models of the Water Heater were com¬ 


the equipment rack 3 in. to shift the dynamotors 
aft by that amount, of mounting the power 
relay on the rack, and of using a reproducer 
head that is less sensitive to stray fields. The 
following description of the apparatus is based 
on the improved design. 


Acoustic and Timing System 

The acoustic system of the Water Heater 
utilizes a magnetic wire reproducer as a signal 
source. Electric impulses from this source are 
amplified and are then converted into sound by 
a loudspeaker. The various components of the 
acoustic and timing system are shown in Fig¬ 
ure 29, and their dimensions and weights are 
given in Table 3. 


Table 3. Dimensions and weights of components 
of acoustic and timing system. 


Description 

1 

Height 

(in.) 

Width 

(in.) 

Length 

(in.) 

Weight 

(lb) 

Equipment rack 

14 

10 

49 

120 

Magazine 

6 

5 

14 

12 

Loudspeaker 

16 

14 

16 

105 

Attenuator 

3 

6 

7 

7 

Waiting time clock 

3.5 

5.25 diam 

4 

Total 




248 


The assembled mine is shown in Figure 30 
as it appears before it is launched. Arrows in¬ 
dicate the location of the loudspeaker compart¬ 
ment near the nose, the equipment rack and 
magazine compartment just forward of the cen¬ 
ter, and the attenuator and waiting time clock 
in the afterbody. The rectangular handhole pro¬ 
viding access to the magazine is also indicated. 

When the mine has been launched and has 
traveled the designated distance, it anchors it¬ 
self and upends so that its axis becomes vertical. 
In this condition it floats with 30 in. of the 


pleted in all. The first model of the Water 
Heater was built and tested before the second 
and third models were constructed. This per¬ 
mitted the incorporation of desirable changes 
in the later models. In the acoustic and timing 
system these changes consisted of reducing the 
weight by the use of aluminum, of lengthening 


forward end projecting out of the water as 
shown in Figure 31. A few minutes before the 
sound program starts the loudspeaker is ele¬ 
vated about 6 ft above the water and is pointed 
in a preset direction as shown in Figure 32. 
Before elevation, the loudspeaker is packed in 
the shell with the horns pointing along the axis 


* 


ONFI AL 















150 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


of the mine, but, as soon as it is elevated clear 
of the shell, a latch is tripped, and the loud¬ 
speaker swings on trunnions under the influ- 


nal voltage is generated in a pickup coil in the 
magnetic wire reproducer. From there it is 
transmitted directly to a 10,000-ohm volume 



rLOUDSPEAKER 


EQUIPMENT RACK AND MAGAZINE 
MAGAZINE HANDHOLE 


ATTENUATOR AND 
WAITI NG TIME CLOCK 


Figure 30. Water Heater prepared for firing. 



Figure 31. Water Heater at anchor. 


ence of gravity so that the horn axis becomes 
horizontal. 

Electric Circuits 

A simplified schematic diagram of the trans¬ 
mission circuit is shown in Figure 33. The sig- 



Figure 32. Water Heater in operating ppsition. 


control at the input of the amplifier and thence 
through the amplifier. The amplifier terminates 
in an output transformer and is capable of 
supplying 500 watts to a 4.5-ohm load. After 
leaving the amplifier, the signal goes through a 
test jack and an attenuator, and finally reaches 


CONFIDENTIAL \ 











THE WATER HEATER 


] 51 


the loudspeaker where it is converted into 
sound. The attenuator is used to adjust the 
sound intensity level. 



Figure 33. Transmission circuit. 


A schematic diagram of power, control, and 
transmission circuits is shown in Figure 34. 
It may be seen that the entire circuit is inactive 
until switch S-12 is closed and the hands of the 


mechanically, starts the program clock, and 
energizes switch S-9. Some minutes later, when 
a moving finger on the program clock closes 
switch S-9, the power relay will operate. This 
closes the power circuits from the battery to 
the reproducer drive, the amplifier, the two 
dynamotors, and the fan. The power relay locks 
itself up electrically through switch S-8 (nor¬ 
mally closed) and the 50-ohm resistor on the 
reproducer. 

The sound reproduction will then start and 
will continue until switch S-8 is opened by 
coming in contact with one of the cams on the 
reproducer time control bar. Opening this 
switch releases the power relay and shuts down 
the reproducing system. (The program clock 
finger has moved on by this time so that switch 
S-9 is again open.) This sequence of operation 
of switches S-8 and S-9 is repeated for each 
part of the sound program. The system may 
also be started by closing toggle switch S-10 


POWER RELAY 



* 


waiting time clock bridge the clock contacts. 
Completing this circuit causes the relay in the 
program clock and also the loudspeaker elevator 
relay to operate. The clock relay locks itself up 


and pushbutton switch S-ll. This is a conven¬ 
ience when testing and adjusting the amplifier. 

Switch S-5 may be used to arm or destroy 
the mine at the completion of the sound pro- 













































































































































152 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


gram. Switch S-7 is a limit switch designed to 
stop the reproducer at the end of the magnetic 
wire. 

A thermostatic delay relay is provided in the 
motor circuit of the reproducer. Its function is 
to permit the amplifier to warm up for 20 sec¬ 
onds before the reproducer is started. 

Magazine 

The magnetic wire reproducer and a program 
clock are built into a magazine that may be 


r- REPRODUCER PROCRAM 

I 



Figure 35. Magazine. 

easily removed from the mine, a special rectan¬ 
gular handhole being provided for this purpose. 
This feature permits taking these components 
to an operating base laboratory where facilities 
are available for recording the sound program 
on the magnetic wire and for setting the pro¬ 
gram time controls. 

A view of the assembled magazine is shown 
in Figure 35. The switch fingers around the dial 
of the program clock and the cams on the re¬ 
producer time control bar are readily accessible. 
Electric connections are made through a mul¬ 
ticircuit jack in the magazine base. Spline 
shafts also project through the base. One of 
them engages a coupling on the reproducer 
drive motor. 

Although the reproducer and the clock are 
thus mounted together, they are, in fact, dis¬ 
tinct pieces of apparatus and must be consid¬ 
ered separately. 

Reproducer 

The reproducer is shown in Figures 36 and 
37. In these views both the outer cover and a 


Permalloy shield have been removed to expose 
the reproducing mechanism. The essential parts 
are about 2 miles of 0.006-in. magnetic alloy 
steel wire (sufficient for a 30-minute record¬ 
ing), two spools, a recording and reproducing 
head assembly including erase coil and wire 
guides, a layer winding mechanism of the fish¬ 
ing reel type, brake bands to maintain tension 
on the wire, and a time control mechanism. 

Before being reproduced, the program mate¬ 
rial must be recorded on the wire exactly as 
described for the Heater in Section 13.2.3, where 
the principles of the wire recorder are ex¬ 
plained. Between recording and reproduction 
and between reproductions it is necessary to 
rewind the wire. To do this, the reproducer 
must be shifted on the recorder so that the 
motor is connected to the other reel. 

The time control mechanism is shown in 
Figure 37. As the spools rotate, a horizontal 
feed screw geared to them causes microswitch 
S-8 to travel along the length of the reproducer 
from right to left. This switch remains closed 
and thus locks up the power relay until its op¬ 
erating pin comes in contact with one of the 
cams along the time bar. When pressure against 
this cam opens the switch, the power relay will 
be released and the system shut down. Thus, if 
a cam is set along the bar so that it just makes 
contact with the switch pin at the completion of 
a section of the recording, the system will stop 
automatically at that point in the program. Ten 
cams are provided, so the program may be di¬ 
vided into as many as ten sections. 

Program Clock 

The program clock is shown in Figures 38 
and 39. It consists essentially of a clock mech¬ 
anism, a microswitch, a relay, and a group of 
aluminum disks mounted on the clock shaft in 
place of a hand. The outer of these disks is a 
dial that is graduated in minutes from 0 to 120. 
It also has a “start” line located 15 minutes 
before zero. The other disks are ten time cams 
and a back plate. Each time cam has a trian¬ 
gular projection at one point on its periphery. 
The dial and back plate are keyed to the clock 
shaft, but the time cams are held only by fric¬ 
tion. The pressure required to clamp them is 
applied by a knurled nut on the shaft. When 


^[FIDE^^B 









THE WATER HEATER 


153 


this nut is loosened, the cams may be rotated 
so that their projections are opposite desired 
points on the dial. A microswitch and operating 
lever are mounted adjacent to the time cams. 


vents it from making more than one revolution, 
and the clock is reset and wound by rotating 
the dial clockwise. A relay is mounted adjacent 
to the clock mechanism. When it operates, it 



Figure 36. Reproducer, cover and shield removed, reverse position. 



DETONATOR 
SWITCH - 


MINUTE 

SCALE 


•'OitM 


MOTOR 

SWITCH 


TIME 

CAM 


PROGRAM 

MICROSWITCH 


CONTROL 
ROD- 


Figure 37. Reproducer, cover and shield removed, forward position. 


As the cams rotate, their projections move the 
operating lever and close the microswitch. 

The dial rotates in a counterclockwise direc¬ 
tion when the clock is running. A stop pin pre¬ 


closes electric contacts in series with the micro¬ 
switch, and at the same time it removes a me¬ 
chanical brake from the clock balance wheel, 
thus starting the clock. The relay locks itself 



















154 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


in the operated position by means of a latch. 
This latch may be released by moving the stop 
lever to the right as viewed from the front of 
the panel. 

The clock is prepared for use by adjusting 
the time cams, setting the relay at normal, and 
setting the dial so that the “start” line coincides 
with the V of the operating lever. The position 
of the time cams is determined by the time 


Reproducer Drive 

Top and bottom views of the reproducer drive 
unit are shown in Figures 42 and 43. The prime 
mover is a 24-volt, % 5 -hp, 5,600-rpm, d-c motor. 
The speed is held constant by a centrifugal 
contact governor that cuts a resistance in or 
out of the motor circuit. The motor is coupled 
to a 10/1 worm-gear speed reducer to obtain 
the required 560 rpm at the reproducer shaft. 



Figure 38. Program clock, front view. 


Amplifier 

The amplifier and amplifier circuit are shown 
in Figures 44 and 45. The voltage from the 
reproducer is fed to volume control P-1 shunted 
by a 0.01-^uf capacitor. This capacitor resonates 
with the coil in the reproducer head and im¬ 
proves the high-frequency response of the sys¬ 
tem. After leaving the volume control, the sig¬ 
nal is amplified by a 6SH7 pentode and then a 
6J5 triode. The output of the triode is trans- 
former-coupled to a 6SL7 used as a push-pull 
triode. The next stage consists of four 6V6 
tubes connected in parallel push-pull. The final 
stage consists of four 805 tubes in parallel 
push-pull, transformer-coupled to the preceding 
stage and to the output. The filament current 


schedule of the sound program. A cam set at 
the dial mark indicates the time each section 
of the program is to start. When mounted in 
the Heater, the closure of the waiting time clock 
contacts energizes the relay. This starts the 
program clock and closes the circuit to the 
microswitch. Fifteen minutes later the zero 
mark on the dial is opposite the V of the oper¬ 
ating lever. The first time cam is normally set 
at this point. Pressure of this or of any other 
cam on the lever closes the microswitch and 
starts the sound system. 

Equipment Rack Assembly 

The equipment rack assembly consists of the 
reproducer drive, the amplifier, the low- and 
high-voltage dynamotors, and auxiliary equip¬ 
ment all mounted on an aluminum rack. This 
rack also holds the magazine when it is in place 
in the mine. Two views of the assembly are 
shown in Figures 40 and 41. 



Figure 39. Program clock, rear view. 

for this power stage is obtained from a 12-volt 
tap on the battery and the 1,400-volt plate 
supply from the high-voltage dynamotor. Fila¬ 
ment current for all other tubes is obtained 
from an 8-volt battery tap, and their plate sup¬ 
ply is from the 300-volt low-voltage dynamotor. 
The plate voltage for the first stages is stabi¬ 
lized and decoupled from the dynamotor by 
voltage-regulator tubes V-8 and V-9. The regu- 


CONFIDENTIALfr 











THE WATER HEATER 


155 


lation of the amplifier is improved by negative 
feedback around the third and fourth stages 
(R-15 and R-16). 

The gain of the amplifier is about 120 db, 
and its output power capacity is 500 watts into 


0.64 ampere. The unit is 6 in. in diameter by 
11 in. long, and weighs 39 lb. 

Minor Equipment 

Air is circulated over the amplifier by an 8-in. 
fan driven by a 24-volt d-c series motor. 



Figure 40. Equipment rack. 


4.5 ohms. Its frequency-response characteristic 
is flat from 300 to 5,000 c. 

Low-Voltage Dynamotor 

The low-voltage dynamotor is one of a stand¬ 
ard design covered by Bell Telephone Labora¬ 
tories specification KS-5558, L2. It is normally 
used on a 28-volt supply and will deliver 0.180 
ampere at 285 to 320 volts. 


MAGAZINE 




Figure 41. Equipment rack with magazine. 


High-Voltage Dynamotor 

The high-voltage dynamotor was designed 
especially for this project. With an input of 
21.5 volts, 60 amperes, it will deliver 1,250 volts, 


The power relay is a 3-pole, single-throw 
switch connected in the circuits between the 
battery and the apparatus on the equipment 
rack. 





















156 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


A test strip is located on the side of the rack 
just below the amplifier. In this position it is 
accessible through the magazine handhole. It 
contains the knob of the amplifier volume con¬ 
trol, the toggle and pushbutton switches for 



Figure 42. Reproducer drive, top view. 

manually starting the acoustical system, the 
test jack by which a resistor load may be sub¬ 
stituted for the loudspeaker, and a toggle switch 
and 24-volt lamp for illumination. 

The 3,000-volt, 0.5-/xf capacitor, C-10, is con¬ 
nected across the output of the high-voltage 



Figure 43. Reproducer drive, bottom view. 


dynamotor to reduce the commutator ripple in 
its output voltage. 

Loudspeaker 

The loudspeaker is exceptionally light and 
compact, measuring 16 by 14 by 16 in. and 
weighing 105 lb. It has a power capacity of 500 
watts, giving a ratio of only 3.3 oz per watt 
capacity. It consists essentially of eighteen re¬ 


ceiver units coupled to nine horns. It is shown 
in Figure 46. 

The horns are made of aluminum. They are 
10 in. long with a 250-c exponential taper and 
have 4.5-in. square mouths. The main housing 
is made of steel. In addition to supporting and 
protecting the receiver unit, this housing pro¬ 
vides magnetic shielding that reduces the stray 
field set up by the receiver magnets. This is 
important as the magnetic compass used to 
orient the loudspeaker is located nearby. The 



Figure 44. Amplifier. 


unit is mounted on trunnions projecting from 
the sides of the housing. They are located di¬ 
rectly above the center of gravity so that when 
swinging freely the horn axes remain hori¬ 
zontal. 

The receiver units assembled in the housing 
are shown in Figure 47. They are grouped in 
subassemblies of two receivers each. The re¬ 
ceivers are of the moving coil type with perma¬ 
nent magnet fields and phenolic impregnated 
fabric diaphragms. A plastic coupler provides 
efficient acoustic coupling betwen the diaphragm 
and the throat of the horn. In the subassembly, 
the two diaphragms face each other and work 


ffQNFTDF.NTTAL \ 







THE WATER HEATER 


157 




CONFIDENTIAL 


Figure 45. Amplifier circuit. 


















































































































































158 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


into a common chamber. They are phased so 
that their effect is additive. 

Each receiver has an impedance of 9 ohms, 



Figure 46. Loudspeaker. 

and the subassembly, consisting of two receiv¬ 
ers in parallel, has an impedance of 4.5 ohms. 



Figure 47. Loudspeaker, cover removed. 


loudspeaker also have an impedance of 4.5 ohms. 
The d-c resistance is about 65 per cent of the 
impedance. This method of wiring provides a 
very dependable loudspeaker as the failure of 
any one receiver simply shifts its load to the 
other five in parallel with it. This results in 
only a negligible decrease in the sound output, 
and the receivers have sufficient marginal power 
capacity to carry the excess load for the short 
time required. 

The relative frequency-response character¬ 
istic of the loudspeaker is shown in Figure 48. 
The dip at 3,800 c is caused by interference 
between the two opposing diaphragms of the 
subassemblies, the effective distance between 



them being one-half wavelength at that fre¬ 
quency. A better low-frequency response would 
be desirable, but this could only be provided by 
increasing the size of the horns, and space 
limitations do not permit it. An electric input 
of 500 watts in the 1,000-c region will produce 
a sound intensity level of 118 db on the sound 
axis 30 ft from the horn mouth. 

The response at 30 degrees off the sound axis 
is also shown in Figure 48. Below 1,000 c, little 
loss in level is produced by moving off the axis, 
but at higher frequencies the loss becomes in¬ 
creasingly greater. These high frequencies are 
of only minor importance in sound deception 
so that the 30-degree response is tolerable. 1 
However, any further lowering of the effective 
high-frequency cutoff would be serious. 


The subassemblies are connected in groups of Attenuator 

three in parallel, and these groups are con- The attenuator is connected between the am- 
nected in series. This makes the assembled plifier output and the loudspeaker. In this cir- 


FIDENTIAL 















































THE WATER HEATER 


159 


cuit location it attenuates the background noise 
by the same amount that it attenuates the signal 
and thus provides the maximum signal-to-noise 
ratio at all sound levels. Also the fact that it 
is a separate unit allows it to be mounted in 
the afterbody where it is most readily accessi¬ 
ble. The arrangement has the disadvantage that 
the attenuator must have a power capacity of 
500 Wyatts. Commercially available attenuators 
do not even approach this rating so a unit had 
to be designed especially for this project. It is 
shown in rear view with cover removed in 



Figure 49. Attenuator, cover removed. 

Figure 49. Two tapped resistor units are used, 
one in series "with the line and one in shunt. 
They are made by wrapping resistor wire in a 
helical groove cut in the outer surface of ce¬ 
ramic tubes. The taps are connected to the 
points of a 9-pole, 2-deck selector switch. The 
resistors are proportioned so that, when the 
switch is rotated, the input resistor remains 
constant at 4.5 ohms but the attenuation varies 
between zero and 40 db in 5-db steps. 

The case is made of anodized copper to pro¬ 
vide maximum heat radiation and is perforated 
to permit air circulation. It is 6 in. square by 
2.5 in. high. Input and output receptacles and 
the switch knob extend beyond these dimen¬ 
sions. 


Waiting Time Clock 

The waiting time clock is an accurate time 
switch that may be set to close an electric cir¬ 
cuit within 1 minute of any desired time within 
12 hours. It is 5.25 in. in diameter by 3.5 in. 
high and weighs 4 lb. It is mounted in the after¬ 
body on the inside surface of a handhole cover. 
This is the same handhole that provides access 
to the attenuator. 

The clock is shown in Figure 50. The hour 
and minute hands and the dial are of a conven¬ 
tional design. The hands may be set to the cor¬ 
rect time by rotating the minute hand the re¬ 
quired number of revolutions in the counter¬ 
clockwise direction. 

The clock is normally prevented from running 
by a spring-wire brake on the rim of the balance 
wheel. This brake is removed and the clock 
starts when the toggle switch shown in the 
figure is thrown to “on.” Operating this switch 
also closes an electric circuit from the connector 
block to a “minute” contact. 

The dial is surrounded by a ring that contains 
an index and a flexible minute contact. The 
ring may be rotated around the dial to place 
the index at any desired position, and it will 


Figure 50. Waiting time clock. 

be held in that position by friction. The contact 
will always be located 15 minutes (90 degrees) 
counterclockwise from the index. An electric 
connection of a few seconds’ duration is made 
between the contact and a pin on the underside 
of the minute hand. 
















160 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


Another ring is located in the central hole in 
the dial. This ring also contains an index and 
a contact, and may be rotated as desired. This 
contact is simply a metal plate set flush with 
the surface of the ring. A spring wiper on the 
underside of the hour hand makes an electric 
connection to this contact when the hand is 
directly over it. Both hands and both contacts 
are gold-plated to assure low contact resistance. 

In use, the inner index is set at the hour and 
the outer index at the minute that the sound 
program is to start. The hands are set at the 
correct time, and the clock is started by oper¬ 
ating the toggle switch. Fifteen minutes before 
the time indicated by the indexes, the hands 
will both be at their contact points. In this 
position a continuous electric circuit is formed 
from one terminal of the connector block 
through the inner contact, the hour hand, the 
minute hand, the outer contact, and the toggle 
switch to the other terminal of the connector 
block. This 15-minute anticipation of the sound 
program allows time to elevate the loudspeaker. 

Recorder 

The recorder is auxiliary equipment used to 
prepare the magazines by imposing the desired 
sound programs on their reproducers. It is 
substantially similar to the recorder employed 
for other Heaters described in Section 13.2.3. 
Other accessories, such as a microphone and 
test set, are also substantially similar. 

Instruction Book 

A book describing the Water Heater and con¬ 
taining instructions for testing, adjusting, and 
operating it has been prepared jointly by Bell 
Telephone Laboratories and General Electric 
Company. 3 The book was written for personnel 
detailed for its particular operation without 
previous knowledge of the device. Thirty copies 
were delivered to the Bureau of Ordnance, U. S. 
Navy. 


13 ' 4 ' 3 Operation of Acoustic System 

Preparation of Magazine 

Tactical considerations will determine the 
content and time schedule of the sound pro¬ 


gram. This program must be recorded on the 
magazine of a Water Heater, and the program 
time controls must be set. This work is done at 
an operating base. 

The magazine is mounted on the recorder. 
The entire length of wire is first erased to as¬ 
sure that no previously recorded signal will 
interfere with the program. The first 30 sec¬ 
onds of wire are recorded with some steady 
test sound derived from an oscillator, phono¬ 
graph test record, or a whistle. The volume 
control is adjusted for this recording so that 
the electric eye volume indicator just closes. 
This produces a fully modulated wire. At the 
end of 30 seconds the volume control is turned 
to zero. The recorder is allowed to operate for 
a few seconds more and then is stopped. The 
next operation is to slide the first cam along 
the time bar (Figure 37) until it just operates 
microswitch S-8. The cam is locked in this posi¬ 
tion by its set screw. 

The first section of the sound program is then 
recorded. The program material may be derived 
from a microphone pickup of “live” sounds 
such as speech, or from previously recorded 
sounds stored on phonograph disks, magnetic 
recorders, or similar devices. During the re¬ 
cording of the program, the volume control is 
adjusted so that the electric eye just closes on 
the peaks of the signal. At the end of this sec¬ 
tion of the program, the volume control is 
turned to zero, the recorder is stopped, and the 
second time cam is adjusted. 

This procedure is repeated for each section 
of the program except the last. The reproducer 
has a capacity of 30 minutes’ total recording 
time, and this may be divided into as many as 
ten sections. At the completion of the last sec¬ 
tion, no time cam is used. Instead, the stop 
collar is locked into position against the micro¬ 
switch bracket. Pressure of the switch bracket 
against this collar will close switch S-5, and, 
at the end of the actual operation, this will 
explode the detonator. 

When complete, the recording is rewound and 
then reproduced by utilizing the playback fea¬ 
ture of the recorder. During this reproduction, 
the quality of the recording is observed, and 
any faulty portions are noted. These portions 
are then erased and recorded again. When fi- 


CONFIDEXTIAU 






THE WATER HEATER 


161 


nally judged satisfactory, the wire is rewound 
to the starting point, and the reproducer is 
ready for use. 

The program clock on the end of the maga¬ 
zine is usually adjusted at the time the record¬ 
ing is made. The clock dial is rotated clockwise 
until the “start” mark is aligned with the oper¬ 
ating lever of the microswitch. This position is 
shown in Figure 38. The operation automat¬ 
ically winds the clock. The central knob is then 
loosened so that the fingers projecting beyond 
the rim of the dial may be rotated. One of these 
fingers is set at the number of minutes after 
H hour that the first section of the sound pro¬ 
gram is to start. Other fingers are set at the 
times subsequent sections are to start, and any 
surplus fingers are stored in the space beyond 
120 minutes. The knob is then tightened, lock¬ 
ing all the fingers in position. The magazine is 
now ready for insertion in the mine. 

Adjustment of Amplifier 

After the magazine has been prepared, the 
cover is removed from the magazine handhole, 
and the magazine is inserted in the mine and 
latched in place on the reproducer drive. The 
test set is then connected to the test jack on the 
equipment rack. Toggle switch S-10 is now 
operated and push-button switch S-ll is closed 
momentarily. This operates the power relay and 
starts the system. Twenty seconds later the 
reproducer motor starts, and the 30-second test 
signal recorded at the start of the wire is re¬ 
produced. During this period, the amplifier vol¬ 
ume control is adjusted so that 500 watts (47 
volts) is delivered to the test set. At the end 
of 30 seconds the test signal stops; a few sec¬ 
onds later the microswitch on the reproducer 
will reach the first time cam, and the system 
will shut down automatically. The test set is 
then removed, the toggle switch restored to 
“off” if this has not been done previously, and 
the handhole cover is secured in place. 

Adjustment before Firing 

The waiting time clock and the attenuator 
are set just before firing. Both of these are ac¬ 
cessible through the port handhole in the after¬ 
body. This location was chosen so that the 
adjustment may be made with only a short 


length of the mine withdrawn from the firing 
tube. The clock indexes are set at the time the 
sound program is to start, the hands are set at 
the correct time at the moment of setting, and 
the clock is started. 

The proper attenuator setting is governed by 
the anticipated sound transmission loss between 
the mine and the shore, and by the sound level 
that is desired on shore. The transmission loss 
is a complex function of distance and of atmos¬ 
pheric conditions, the most important condi¬ 
tions being wind speed and direction. The de¬ 
sired sound level on shore depends on the objec¬ 
tives of the operation. For deceptive purposes 
the optimum sound intensity level has been 
found to be about 15 db above the steady mask¬ 
ing noise. These factors are discussed at length 
in reference 1 and have been summarized in 
Section 13.1. Table 4 shows the attenuator set¬ 
ting to produce 15 db above masking noise for 
sound programs transmitted over a range of 
distances under a variety of wind conditions. 
Some inaccuracy is tolerable because the trans¬ 
mission loss varies considerably from moment 
to moment. The transmission of intelligible 
speech requires a higher sound level on shore 
than do deceptive sounds. The attenuator should 
be set at step 9 (no attenuation) for this pur¬ 
pose, and the maximum range should be the 
distance specified in the table for step 7. 

The proper attenuator setting is thus deter¬ 
mined by a combination of the mission, the 
acoustic range, and predicted weather condi¬ 
tions. The attenuator is set at that point and 
the handhole secured. From this point on, the 
action of the acoustic and timing system is 
entirely automatic. 


13-44 Performance of Acoustic System 

The acoustic system of the Water Heater has 
an effective frequency range of 350 to 5,000 c. 
This is ample for the reproduction of speech 
and is adequate for the reproduction of many 
tactical sounds. However, those sounds which 
are rich in low-frequency components are not 
faithfully reproduced, and in deceptive warfare 
they must be used cautiously to avoid detection. 
In particular, the sound level on shore must be 


CO NF i; ' 1 ' 





162 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


kept low so that the observer is forced to strain 
to hear it. Under conditions of strain and of 
poor visibility, the observer’s imagination will 
cause him to ignore deficiencies in the sound. 1 

The maximum distance that the sound is ef¬ 
fective depends upon the weather, 1 the wind 
speed and direction being the most important 
factors. This effect is shown by Table 4. Under 
favorable conditions the useful range is 6,000 
yd, but under adverse conditions it may be re¬ 
duced to as short as 1,000 yd. The effective 
spread of the sound is approximately ±30 de¬ 
grees from the sound axis. 


13.4.5 General Assembly of Water 
Heater 

The outline of the Water Heater is shown in 
Figure 51. Various parts are designated as fol¬ 
lows: 

No. 1 Anchor, or nose assembly. 
No. 2 Speaker and elevator com- 


Section 

Section 

partment. 

Section 

partment. 

Section 


No. 3 Amplifier and battery com- 
No. 4 Afterbody, or propulsion 

equipment. 

The complete unit weighs 2,700 lb, and when 
in salt water it has a negative buoyancy of 150 
lb. After the anchor, which weighs 550 lb, has 
been dropped, the buoyancy becomes positive, 
and the Water Heater therefore floats to the 
surface. It will ride with its axis vertical be¬ 
cause the loss of the nose weight shifts the 
center of gravity aft of the center of buoyancy. 

Tests showed that a glide angle of approxi¬ 
mately 2% degrees was desirable in order to 
maintain stability during the Water Heater’s 
run. The Heater is therefore designed nose 
heavy with the center of gravity 135 in. from 
the aft end. It is trimmed by the addition of lead 
in either section No. 1 or section No. 4 or both. 
Throughout the design of the device, it was nec¬ 
essary to take special cognizance of the total 
and of the distribution of weight so that the 
completed unit could be trimmed by a small ad¬ 
dition of weight. 

Corrosion-resistant metals, plating, and trop- 
icalization have been used throughout the equip¬ 


ment whenever possible to provide protection 
against the salt atmosphere. 


13-4-6 Component Parts 

Shell 

The shell of the Mark 18 torpedo, being 21 ft 
long by 21 in. in diameter, was the largest of the 


Table 4. Attenuator settings to produce 15 db 
above masking noise on shore. 


Distance (yd) 

Calm 

Wind speed (knots) 

1-3 3-6 6-12 12-22 



Wind angle 0° to 90° 

400 

1 

1 

2 

2 

4 

600 

1 

2 

2 

3 

4 

800 

2 

2 

3 

4 

5 

1,000 

2 

3 

3 

4 

5 

1,200 

3 

3 

4 

4 

6 

1,400 

4 

3 

4 

5 

6 

1,600 

4 

4 

4 

5 

6 

1,800 

5 

4 

5 

5 

7 

2,000 

6 

4 

5 

6 

7 

2,500 

7 

5 

6 

6 

8 

3,000 

9 

5 

6 

7 

8 

3,500 


6 

7 

8 

9 

4,000 


7 

8 

8 


5,000 


8 

9 



6,000 


9 







Wind angle 135° 


400 


2 

3 

4 

4 

600 


3 

4 

5 

5 

800 


4 

5 

6 

6 

1,000 


5 

6 

7 

7 

1,200 


6 

7 

8 

8 

1,400 


7 

8 

9 

9 

1,600 


8 

8 



1,800 


8 

9 



2,000 


9 







Wind angle 180° 


400 


3 

4 

4 

5 

600 


4 

5 

6 

7 

800 


5 

6 

7 

8 

1,000 


7 

8 

8 

9 

1,200 


8 

9 



1,400 


9 





easily handled variety. It provided sufficient vol¬ 
ume and buoyancy to house all of the contem¬ 
plated components. Each section was made by 
wrapping % 6 -in. plate around pressed ribs and 
welding, with machined joint rings at the end 
for connection to the following section. 


Confidential j 









THE WATER HEATER 


163 


The position of handholes is critical since 
access must be made at the proper points. 

Power Supply 

The power requirements for propulsion for 
15 minutes and for operation of the acoustic 
system for 30 minutes were calculated, and the 
Electric Storage Battery Co. provided a battery 


weight of the entire battery assembly is ap¬ 
proximately 500 lb. 

The upending of the battery was made pos¬ 
sible by using a large cap of special design, suit¬ 
able for catching electrolyte, by the use of the 
proper quantity of electrolyte in relation to 
available space, and by careful calking of all 
joints. Tests showed that the battery supplied 



t 

o 

o 



TO SET* 20 TURNS 200 YDS STARBOARD SAME EXCEPT "ON-OFF” 
PER TURN 1000 TO R AND L ARE REVERSEO PRIMING 
5000 YDS TO SETs 5*PER TURN SWITCH 

90°MAX RIGHT 
OR LEFT 



FIG 4 FIGS 


TO SETs 3 TURNS 10 FEET TOP RUDDER AND PORT 
PER TURN ELEVATOR MARKINGS 

20*50 FEET (5* MARKSJ 


Figure 51. Water Heater outline. 


in three sections capable of delivering the neces¬ 
sary power even in the upended position in 
which it must operate after the device has 
anchored itself. The three sections are con¬ 
nected in parallel during the period of propul¬ 
sion and then switched by a series-parallel re¬ 
lay, developed especially for the job, to series 
connection for the remainder of the operation. 
The aft section has greater capacity than the 
other two to provide the additional control 
power needed for the afterbody controls. The 


all the necessary power but with no safety fac¬ 
tor. 

Propulsion Equipment 

The propulsion equipment is part of the Mark 
27 torpedo and is therefore described only 
briefly. It consists of firing switch, motor¬ 
starting relay, distance-setting unit for the pro¬ 
pulsion motor, distance gear, propeller shaft, 
and propeller. The firing switch is activated by 
a dog in the firing tube. The propulsion motor 
















































































164 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


is a 4-pole compound-wound, 7.75-hp, 1,800- 
rpm, d-c motor rated on a 15-minute special 
duty basis, requiring 103 amperes at 67 volts. 



COVER BOLT 
GASKET 

COVER BOLT 


Figure 52. Anchor. 

The control system governs the depth and di¬ 
rection of the run. Both functions operate on 
the selsyn principle, which yields small poten- 



Figure 53. Anchor assembly to section No. 2. 

tial differences that are proportional to the dif¬ 
ferences between the Water Heater’s actual po¬ 
sition and the predetermined control settings. 


The depth control, located at the top of the 
afterbody shell, is set to the desired depth of 
run by means of a calibrated disk and index. 
Water pressure acting on the bellows of the 


BRAKE ADJUSTMENT RE~ WIND 



BRAKE DRAG BRAKE DISTANCE 

ON-OEF ADJUSTMENT LEVER SET 


Figure 54. Anchor reeling mechanism. 

depth control causes a rotation of the depth 
selsyn. A pendulum damping assembly prevents 
the Heater from plunging or rising too sharply. 

The direction is controlled by a gyroscope set 
either for dead ahead or for an angle course. 
One of the windings of a selsyn is mounted on 
the gimbals of the gyroscope and the other on 
the stator. This selsyn is interconnected with 



Figure 55. Squib bolt assembly parts. 


another on the angle fire setting spindle. The 
upending of the Water Heater created a new 
problem since the sudden change of direction 
placed such a stress on the gyroscope that the 
motor shafting flexed enough to snap the arma¬ 
ture leads. A special gyroscope was developed 
to withstand this unusual strain. 

The error of direction may amount to ±2.87 


























THE WATER HEATER 


165 


degrees. The error is caused by precession of 
the gyroscope during the time of traveling the 
course. A distance error of 100 yd or 5 per cent 
of the set distance, whichever is greater, re¬ 
sults from using the number of screw revolu¬ 
tions with its inherent errors as the basis of de¬ 
termining the distance at which the propulsion 
motor is stopped. 

Anchor 

The anchoring mechanism consists of the 
anchor, shown in Figures 52, 53, and 54, and 



UP LIMIT 
SWITCH 


CABLE PULLEY 


"OOWN" LIMIT 
SWITCH 


Figure 56. Elevator mechanism. 

the explosive release bolts shown in Figure 55. 

The release bolt consists of a steel block 
drilled to slide in a threaded boss far enough to 
pin it in place by a shear pin. A six-grain charge 
of powder, in the form of a squib, is placed 
behind the boss and, when detonated, expels the 
boss which is carried off by the falling anchor. 
In this way, a means of dropping anchor at any 
desired time is provided. 

The anchor consists of an exterior iron cast¬ 
ing, weighing 450 lb, a cable reel and its associ¬ 
ated mechanism, shown in Figure 54, a cover 
plate to protect this mechanism, and a gasket 


to seal this plate against section No. 2. The 
whole assembly weighs 550 lb. 

The anchor cable used is % in. in diameter 



ELEVATOR ORIENTING 

CONTROL MOTOR ELEVATOR 

SWITCHES CONNECTOR RESISTOR MOTOR RELAY 


CONNECTOR ELEVATOR VIBRATOR 

MOTOR RESISTOR 


Figure 57. Elevator mechanism control panel 
interior. 

and made of 19 strands of best cable steel. The 
cable is fastened to the Water Heater at about 



Figure 58. Elevator mechanism control panel in 
place. 

the center of section No. 3. The cable then 
passes through a groove in the shell, flush with 
the outside diameter, through a similar groove 












166 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


in part of the anchor, through the pay-out slot, 
and onto the drum, where 1,000 ft of the cable 
is stored. Just before reaching the drum, how¬ 
ever, the cable is spliced by a swing link, per¬ 
mitting the anchor cable to be detached from 
the Water Heater during recovery operations or 
for other reasons. 

The drum is restricted by a brake band, 
which not only maintains a drag during unreel- 


LOUDSPEAKER 


LOUDSPEAKER 

LATCH 



SQUIB BOLTS 


—LIFTING CLAMP 


Figure 59. Loudspeaker fully raised. 

ing, but also stops the pay-out at a set length 
of cable. This stop is effected by a gear train 
from the drum to a lead screw which advances 
1 turn for every 16 turns of the drum. On the 
lead screw is a cam, and, when this cam comes 
in contact with a stationary brake lever, a 
series of linkages tightens the brake band on 
the drum and unreeling stops at the length se¬ 


lected. The brake lever is set at 300, 600, or 900 
ft of cable by an exterior adjustment. Rotation 
of this control slides the brake lever to the cor¬ 
rect position. 

Elevator 

The elevator mechanism is housed in section 
No. 2 and serves to hoist the orientation and 
loudspeaker equipment out of the shell for op¬ 
eration. It is shown in Figures 56, 57, and 58. 
The structure consists of a three-cornered cast- 
aluminum platform, below which three pipes 
are fitted and pinned. The three stainless-steel 



ORIENTING 
C.W T r.M 


SPLASH LOUDSPEAKER 
PLATE SUPPORT 
GASKET GUIDE MOTOR 


SOUl 6 SQUIB 

TERMINAL SADDLE 
BLOCK 


LOUDSPEAKER AMPLIFIER COVER 
LATCH 


Figure 60. Orienting mechanism with cover off. 

pipes pass through bearings held by a plate 
bolted to the inside of the shell in such a way 
that, when the pipes are lifted from below, the 
whole assembly is free to rise. It is held in the 
vertical position by double bearings. 

The hoisting apparatus consists of a small 24- 
volt d-c motor with a gear reduction which 
drives a drum. Three separate Ym-in. steel 
cables are fixed to this drum and pass over re¬ 
spective pulleys at the three pipe bearing points, 
thence down over pulleys at the bottom of each 
pipe, and back up to the fixed bearing points. 
When the drum rotates, each cable is wound 













THE WATER HEATER 


167 


equally on the drum, thereby shortening the 
cable and raising each of the three pipes simul¬ 
taneously. The elevator is lowered by reversing 
the d-c motor and consequently unreeling cable 
from the drum. Initial tension on each cable is 
adjusted by a movable eye at the fixed end of 
each cable. 

Notches are cut in each pipe to operate limit 
switches at various positions of the elevator, 
and a mechanical lock is automatically engaged 



SQUIB SADDLE COMPASS SETTING PHOTOCELL 

AND SOCKET 


SET SCREW 

Figure 61. Orienting mechanism compass as¬ 
sembly. 

when the elevator is fully raised to prevent low¬ 
ering during operation. 

The upper portion of the platform carries a 
circular disk slightly smaller in diameter than 
the shell, to which is attached a flexible cylin¬ 
drical rubber boot. The lower end of the boot is 
fastened to a ring on the inside of the shell mid¬ 
way in the elevator platform’s travel. The boot 
is sealed with cement, top and bottom, thereby 
making a watertight barrier to the interior of 
the Heater and yet allowing the elevator to 
travel up and down. The material of the boot is 


preformed before and during the curing cycle 
so that it tends to keep against the shell and 
away from the elevator. A restricted breather 
(Figure 59) relieves the vacuum created within 
the shell as the elevator rises. (The pressuriz¬ 
ing intake is placed forward of the boot so that 
the pressurizing aids in forcing it well down 
before launching.) 

The platform also has a boss and bearing sur¬ 
face at its center for the support of the orient¬ 
ing mechanism. This serves as the fulcrum for 
the rotation of the loudspeaker and, although 
above the rubber boot, is watertight at the 
bearing surfaces. 

Orientation Mechanism 

The orientation mechanism (Figure 60) 
causes rotation of the loudspeaker support with 
respect to the boss on the platform. Power con¬ 
nections are made through slip rings mounted 
at the center bearing. Orientation is based on a 
magnetic compass. The accuracy of the compass 
is impaired by stray magnetic fields from the 
loudspeaker and by the declination, so that an 
error of ±10 degrees must be anticipated. A 
calibration chart made for each Heater at a 
given location will allow accurate correction, 
but for normal operating conditions the 10-de¬ 
gree error is tolerable since the sound beam 
spreads over a 60-degree angle and is moder¬ 
ately effective throughout a sector of 120 de¬ 
grees. The compass assembly is shown in Fig¬ 
ure 61. When the compass drum at the control 
panel is rotated, the whole compass assembly 
rotates correspondingly. (An automatic stop 
prevents more than one complete turn, thereby 
protecting the wiring against fouling.) 

The compass needle consists of a circular 
disk in which a slot has been cut at the outer 
edge on an arc of about 90 degrees. This slot 
lines up with a beam of light projected from a 
Mazda lamp on the outside top through a lens, 
and, when the slot is directly below this beam, 
the beam passes through, then through another 
lens at the bottom of the compass bowl, and 
falls upon a photocell. The magnetic card re¬ 
mains in a fixed direction. If the compass bowl 
moves far enough, the light will not line up with 
the slot, and light is cut off from the photocell. 

The photocell is used to control the bias on a 


♦ 





168 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


6J5 tube so that plate current flows when the 
cell receives light, and is cut off when the light 
is cut off. The plate current is in turn used to 
activate a sensitive relay which is normally 
closed but has a double-throw contact arrange¬ 
ment. Thus, if light reaches the photocell, the 
relay is closed in one direction, and if light is 
cut off, it closes in the opposite direction. 

This relay action is utilized to control a small 
24-volt d-c motor which is mounted on the 
orientation box but is geared to the aluminum 
platform on the elevator. Operation of the 
motor revolves it and the entire mechanism 
around the bearing at 7.5 degrees per second. 

The design of this circuit requires that the 
motor always be operating either in one direc¬ 
tion or the other, resulting in a constant hunt¬ 
ing action of 2 degrees. This will occur about 
one edge of the slot in the compass card, giving 
an on-off light to the photocell. Polarity of the 
d-c driving motor is therefore important, for, if 
reversed, hunting will immediately take place 
at the other end of the slot and therefore point 
the loudspeaker about 90 degrees away from 
the desired setting. b 

Disposal Unit 

A circuit has been provided to detonate an 
explosive after the completion of the acoustic 
program. The explosive consists of plugs of 
TNT held by brackets against the shell of the am¬ 
plifier section. Following the recommendations 
of the Naval Ordnance Laboratory, a Mark 1 
booster plus a Mark 143 fuze are both housed 
together in a cylinder. The Mark 143 fuze con¬ 
tains both an arming circuit and a firing circuit. 
The arming circuit is closed by the waiting 
time clock at the time the elevator starts. Thus 
the charge becomes armed only after reaching 
its destination. The firing circuit is interlocked 
to prevent premature firing. Before reaching 
the time switch on the reproducer, the circuit 
must be closed by the operation of the distance 
switch in the afterbody (i.e., after the Heater 
has reached its destination) and also through 
a “test” plug which is operated by personnel be¬ 
fore launching. 

b The manufacturer of the compass has expressed the 
opinion that, for further production, they would prefer 
to develop a special compass which would materially 
simplify the present construction. 


The amount of TNT employed is sufficient to 
blow a hole in the side and let the Water Heater 
sink. 

PlNGER 

To facilitate recovery of the Water Heater 
during tests when it might accidentally sink to 
the bottom, a pinger is mounted in the main 
battery compartment. It is turned on at the time 
the priming switch is operated. It consists of a 
45-kc oscillator and a crystal-type hydrophone 
for transforming the electrical pulses into me¬ 
chanical vibrations. The pinger operates on its 
own batteries within its watertight case and 
will operate for several days. The mechanical 
vibrations can be detected by a diver or surface 
craft and are a very effective guide to recovery. 

Leakage Control 

Before launching the Water Heater, it is 
pressurized through the inlet in the anchor and 
soap-water is applied to all joints and hand¬ 
holes. Leaks are thus discovered, and also the 
rubber boot is pushed down to its proper posi¬ 
tion. 

At the moment of dropping anchor, the en¬ 
tire orienting mechanism is exposed to the 
water except for the splash plate. This plate is 
reasonably watertight, but is not a bulkhead 
since it has to be pushed off by the elevator as it 
rises. The time required for rising to the sur¬ 
face after dropping anchor is less than 10 sec¬ 
onds, however, and only a small amount of 
water is shipped. Nevertheless, on upending, 
this water is caught in the cavity and may seep 
through various bearings in the elevator and 
must therefore be caught. A sump has been 
provided to do this, with a drain cock for 
emptying when reconditioning. 


Operation 

When all controls have been set, reproducer 
magazine installed, handholes closed, and the 
entire device tested for leaks by pressurizing, 
the Water Heater may be fired from a conven¬ 
tional submerged tube. Two minutes before 
actual firing, however, the priming switch (Fig¬ 
ure 51) must be rotated to “on.” 


CONFIDENTIAL < 







THE WATER HEATER 


169 


With the closing of the priming switch, the 
pinger is turned on, and the gyro in the after¬ 
body starts. The gyro will reach normal speed 
in the 2 minutes’ delay before firing. 

As the torpedo leaves the firing tube, a dog in 
the tube operates the firing switch (Figure 62). 
This switch releases the gyro lock, thereby free¬ 
ing the rotating element of its support, ener¬ 
gizes the series-parallel battery relay, and 
closes the main propulsion motor relay. 

The device then travels to a spot determined 
by the control settings. At this point, the revolu¬ 
tion counter on the shaft operates the distance 
switch which stops the propulsion gear, ener- 



RUDDER -- 


SETTING SOCKET 

ELEVATOR 
GREASE FITTING 
CONE 


STABILIZER- 


DISTANCE SETTING SOCKET 
FIRING 


LOCK 


PROPELLER 

NUT 


Figure 62. Afterbody interior. 

gizes the explosive release bolts at the anchor, 
turns elevators to “hard-up,” and deenergizes 
the series-parallel relay on the main battery. 

The anchor falls off the nose when the four 
squib bolts explode and pays out cable as it 
falls. When this weight is lost, the remainder 
of the Water Heater becomes positively buoyant 
and floats to the surface, where it remains 
anchored and floating vertically with about 3 
ft of freeboard above the water’s surface. In¬ 
take of splash water is prevented by the splash 
plate. 

At the set hour for performance, the waiting 
time clock in the afterbody makes contact and 
starts the elevator motor and the program 
clock on the recorder magazine. It also ener¬ 
gizes the solenoid circuit of the disposal unit, 
thereby priming it ready for detonation. The 
elevator motor then operates the cable drum 


and lifts all three elevator rods, pushing off the 
splash plate and starting the assembly up¬ 
wards. As the elevator rises, a vacuum is pro¬ 
duced within the rubber boot fastened between 
the elevator and shell, but this is relieved by the 
vent shown in Figure 59. This partial vacuum 
assists in keeping the boot drawn downward 
and hence out of the way of the elevator as it 
rises. 

When the elevator has risen high enough, a 
trip mechanism (see Figure 59) allows the 
loudspeaker to fall free in its bearings and 
point in the horizontal direction. Slightly higher 
in the elevator’s course, the 24-volt power is 
applied by the first limit switch which falls into 
a notch in one of the elevator rods. This ener¬ 
gizes the vibrator (high-voltage supply) and 
the orienting motor. The same limit switch, 
being double-throw, opens one of the squib 
lines. A small increase in elevation trips a sec¬ 
ond limit switch when it falls into the same 
notch on the elevator rod. This applies 12-volt 
power to the Mazda lamp on the compass con¬ 
trol. This limit switch also opens the other 
squib lead. The elevator then continues to rise 
to its full height, when a third limit switch 
opens the relay to the elevating motor and ele¬ 
vation ceases. Also at this time the mechanical 
lockup (Figure 58) snaps into place and pre¬ 
vents the elevator from slipping back down. 

Fifteen minutes after the waiting time clock 
has closed, and independent of the elevator pro¬ 
cedure, the program clock on the recorder mag¬ 
azine (started when the waiting time clock 
closed its contacts) starts the acoustical system 
by closing the main relay (see Figure 34). This 
starts the dynamotors, applies filament power, 
and also energizes the delay relay which subse¬ 
quently starts the wire recorder. The output 
from the amplifier then travels through the 
attenuator in the afterbody and back up 
through slip rings in the orientation mechanism 
to the loudspeaker. For 2 hours the program 
clock governs the production of sound previ¬ 
ously recorded on the wire recorder. During 
quiet periods the clock shuts off the main relay, 
deenergizing all audio equipment, but orienta¬ 
tion continues. 

When 2 hours have elapsed, the program 
clock closes S-5 and energizes the detonator, 


E IAI 







170 


MOBILE LOUDSPEAKING SYSTEMS FOR DECEPTION AND DECOY 


which, if attached, blows a hole in the side, and 
the Water Heater sinks. 

13.5 tactical considerations 

The process of deceiving the enemy’s ears is 
not an exact science, but great strides have been 
made toward removing the guesswork from it. 
In moving rapidly toward combat with sonic 
equipment patterned after the early NDRC 
model, the Navy showed strong confidence in 
their ability to deceive the enemy by suggestive 
caricature of sounds of military interest. 

One important factor bearing upon this ques¬ 
tion is the effect of battle strain on the acumen 
of an observer. Reliable data on this can be pro¬ 
vided only by the accumulation of observations 
made in actual combat zones, and such infor¬ 
mation is not available for this report. How¬ 
ever, the importance of strain in the creation of 
illusions is an elementary psychological fact. 
Such errors of perception are less likely to 
occur when the sound is loud and sustained for 
then it is more readily identified. It is only 
when the exciting stimulus is vague that the 
imagination is given free rein. 

Another well-known psychological fact of in¬ 
terest in deception is the association of stimuli 
received through several senses, for example, 
sight and hearing. If one is accustomed to both 
seeing and hearing a group of boats, he will, 
upon hearing such sounds and looking in the 
direction from which the sounds come, believe 
he sees the boats although there is actually not 
enough light to do so. Therefore, an observer, 
under the strain of impending attack and under 
conditions of poor visibility, such as moonlight 
or dawn, will transform a suggestive noise, 
faintly heard, into a strong illusion of a concen¬ 
tration of enemy forces and may firmly believe 
that he sees as well as hears them. 

Cognizant of the limitations of the early 
equipment, the Navy took full advantage of 


these psychological factors in the development 
of their tactics. In particular, they make the 
sound sporadic and keep it at a level that forces 
the observer to strain to hear it. Good use is 
made of the old theatrical adage that “the most 
profound noise is silence.” Straining gaps of 
silence are, therefore, important parts of their 
tactics of sonic deception. Any attempt at sus¬ 
tained deception might prove its undoing. As a 
result, deceptive operations with the early 
equipment must be confined to an alerting ac¬ 
tion. An attempt to confirm an attack by sonic 
means might well be suicidal. 

Both the Army and the Navy have been mov¬ 
ing progressively toward equipment which per¬ 
mits a greater flexibility in tactics. The major 
improvements involve closing the gap between 
the performance of the first Heaters and the 
minimum requirements for comprehensive 
sound deception established by the combined 
Army, Navy, and NDRC work. High-powered 
high-fidelity systems can, when properly used, 
provide a sonic illusion of a complete attack 
sequence (excluding the simulation of fire). 
With faithful reproduction much less depend¬ 
ence is placed on an observer’s imagination, 
and continuous sound programs become feas¬ 
ible. 

The subject of associated deceptive measures 
is not covered by this work, although, in con¬ 
junction with the Army Experimental Station, 
several tactical problems have been worked out 
with supporting deception from other sources. 
These include smoke screens, explosions, live 
fire, and visual deception. Anything is useful 
that will force an observer to place greater de¬ 
pendence upon his ears or that will offer him 
some confirmation of what he thinks he hears. 

Sonic deception in conjunction with other de¬ 
ception devices is not intended to replace the 
usual phases of a military feint. Its value lies in 
its intelligent use in support of such feinting 
operations. 



GLOSSARY 


HR. Hays carbon dioxide recorder. 

LNR. Leeds and Northrup carbon dioxide recorder. 
Orsat. A portable gas-analysis apparatus which con¬ 
sists of a measuring buret and three or four gas- 
absorption pipets connected by a manifold. 


Q. A figure of merit for a circuit, proportional to the 
ratio of the energy stored to the energy dissipated 
per cycle. 

RR. Ranarex carbon dioxide recorder. 


CONFIDENTIAL 


171 

















































BIBLIOGRAPHY 


Numbers such as Div. 17-310-MI indicate that the document listed has been microfilmed and that its 
title appears in the microfilm index printed in a separate volume. For access to the index volume and to 
the microfilm, consult the Army or Navy agency listed on the reverse of the half-title page. 


Chapter 1 

DEPARTMENT OF TERRESTRIAL MAGNETISM 

1. [Development and Test of Magnetic Compasses and 
Odographs in Vehicles], A. G. McNish, James M. 
Barry, Bryant Tuckerman, and others, OSRD 
1398, Progress Report on Contract NDCrc-187 for 
the Period June 30, 1942 to February 28, 1943, 
Carnegie Institution of Washington, Feb. 28, 1943. 

Div. 17-310-MI 

la. Ibid., Figures 1 through 10. 

lb. Ibid., Report on Tests of June 3 to August 25, 
194.2, on Odograph Installation in Light Tank, 
Sept. 7, 1942. 

lc. Ibid., Report on the Odograph Installation in 
Medium Tank M4A1E2 No. 6, Sept. 23, 1942. 

l d. Ibid., Report on the Odograph Installation in 
B-18-B Army No. 7561, Oct. 8, 1942. 

le. Ibid., Report on the Demonstration of Odo¬ 
graph in Aeroplane on October 9, 1942, Oct. 
10, 1942. 

l f. Ibid., Memorandum on Odograph Tests at Fort 
Knox in Medium Tank M4A1E2, Feb. 22, 1943. 

lg. Ibid., Land, Sea, and Air Logs, Feb. 28, 1943. 

lh. Ibid., Report on Installation of an Odograph 
in B-24D Bomber, Feb. 28, 1943. 

2. Report on Trip to England, November 12, 1942 to 
February 1, 1943, including Demonstration of the 
Odograph, British Aircraft Compasses, British 
Vehicular Compasses, British Dead-Reckoning De¬ 
vices, and British Marine Logs, Bryant Tucker¬ 
man, OSRD 1470, Service Project NDCrc-187, 
Carnegie Institution of Washington, Mar. 31, 1943. 

Div. 17-313.12-MI 

3. Tests of Odograph in Halftrack, Fort Belvoir, 
Virginia [Report Covering Period from], April 8, 
1943 to May 5, 1943, James M. Barry, OSRD 1614, 
Service Project NDCrc-187, Carnegie Institution 
of Washington, June 15, 1943. Div. 17-313-12-M3 

4. Report on Installation of Odograph in T-15 Cargo 

Carrier [Report Covering Period from], January 6 
to March 15, 1943, J. L. Dalke, OSRD 1613, Service 
Project NDCrc-187, Carnegie Institution of Wash¬ 
ington, June 19, 1943. Div. 17-313.12-M4 

5. Tests of Odograph in M-29 Cargo Carrier, Cargo- 
Carrying Sled, and Special Trailer [Report Cover¬ 
ing Period from], October 26, 1943 to January 7, 
1944, James M. Barry, OSRD 3340, Service 


a This list includes all material consulted in the 
preparation of this report. Specific references in the 
report do not necessarily include all items. 


Project NDCrc-187, Carnegie Institution of Wash¬ 
ington, Apr. 1, 1944. Div. 17-313.12-M5 

6. Tests of Odograph in a 2V2-Ton Amphibious Truck, 

James M. Barry, OSRD 4239, Service Project 
NDCrc-187, Carnegie Institution of Washington, 
May 16, 1944. Div. 17-313.12-M6 

7. Installation of Aerial Odograph in 0A10 43-43843, 
William Finley Wright, E. S. Hughes, and A. G. 
McNish, OSRD 3785, Service Project NDCrc-187, 
Carnegie Institution of Washington, June 10, 1944. 

Div. 17-313.11-MI 

8. Tests on Aerial Odograph in PBM-3S, No. 01677 
[During the Period from], December 10, 1943 to 
January 28, 1944, at U. S. Naval Air Station, 
Quonset Point, R. /., Vaughn L. Agy, OSRD 3795, 
Service Project NDCrc-187, Carnegie Institution 
of Washington, June 12, 1944. Div. 17-313.11-M2 

9. Report on Tests of Aerial Odograph in RA-29 at 
Wright Field, Dayton, Ohio, from February 2,1944 
to April 13, 1944, Vaughn L. Agy, OSRD 3805, 
Service Project NDCrc-187, Carnegie Institution 
of Washington, June 14, 1944. Div. 17-313.11-M3 

10. The Department of Terrestrial Magnetism Marine 

Speedometer, R. J. Duffin, OSRD 3338, Service 
Project NDCrc-187, Carnegie Institution of Wash¬ 
ington, June 30, 1944. Div. 17-323.51-MI 

11. A 400 -Cycle Inverter for Operating a Magnesyn 

Remote-Indicating Compass from 110 Volts Alter¬ 
nating Current or Direct Current, Bryant Tucker¬ 
man and Max Malin, OSRD 4240, Service Project 
NDCrc-187, Carnegie Institution of Washington, 
Sept. 16, 1944. Div. 17-314-MI 

12. The Step Writer, R. J. Duffin, OSRD 4731, Service 

Project NDCrc-187, Carnegie Institution of Wash¬ 
ington, Feb. 28, 1945. Div. 17-313.3-M2 

13. The Pedograph, J. L. Dalke, OSRD 4730, Service 

Project NDCrc-187, Carnegie Institution of Wash¬ 
ington, Feb. 28, 1945. Div. 17-313.3-MI 

14. Magnetic Fields of Tanks and Other Vehicles, 
A. G. McNish, Bryant Tuckerman, Vaughn L. Agy, 
and James M. Barry, OSRD 4734, OEMsr-151, 
Service Project OD-46, Carnegie Institution of 
Washington, Feb. 28, 1945. Div. 17-122.2-MI 

15. The Vehicular Odograph, A. G. McNish, Bryant 
Tuckerman, and Vaughn L. Agy, OSRD 4965, 
Service Project NDCrc-187, Carnegie Institution of 
Washington, Apr. 10, 1945. Div. 17-313.12-M7 
15a. Ibid., pp. 29-41. 

15b. Ibid., p. 35. 

15c. Ibid., p. 39. 

15d. Ibid., p. 24. 

16. Final Report on Contract NDCrc-187 and Supple¬ 
ments, J. A. Fleming and A. G. McNish, OSRD 


173 




174 


BIBLIOGRAPHY 


4997, Service Project NDCrc-187, Carnegie In¬ 
stitution of Washington, Apr. 27, 1945. 

Div. 17-310-M2 

17. True Air Mileage Devices, William Finley Wright, 
Vaughn L. Agy, and E. S. Hughes, OSRD 5016, 
Service Project NDCrc-187, Carnegie Institution 
of Washington, Apr. 28, 1945. Div. 17-313.2-MI 
17a. Ibid., p. 10. 

18. Letter to William H. Crew [on Magnetic Com¬ 

passes], Memorandum on Work Conducted at the 
Department of Terrestrial Magnetism, Carnegie 
Institution of Washington, under Division CS 
(Photographs Attached), J. A. Fleming, Service 
Project NDCrc-187, Carnegie Institution of Wash¬ 
ington, Oct. 2, 1945. Div. 17-310-M3 

GENERAL MOTORS CORPORATION 

19. Demagnetizing Military Vehicles, Wayne T. 

Sproull, Preliminary Report PI-77, Project PI- 
4-R, Jan. 12, 1943. Div. 17-315-MI 

20. The Development and Tests of an Inductor Com¬ 
pass, C. E. Grinstead, OSRD 3002, OEMsr-1121, 
Report PI-104, Nov. 18, 1943. Div. 17-312-MI 

21. Tests of Magnetic Eraser for Military Vehicles at 

Proving Grounds and at Washington, D. C., Wayne 
T. Sproull, OSRD 3202, OEMsr-1121, Report PI-99, 
Jan. 5, 1944. Div. 17-315-M2 

22. The Development and Tests of an Inductor Com¬ 
pass [covering period from], December 1943 to 
May 1944, C. E. Grinstead, OSRD 4196, OEMsr- 
1121, Progress Report PI-119, Aug. 31, 1944. 

Div. 17-312-M2 

23. Inductor Compass Tests on an M-3A1 Light Tank, 
June to July 1944, C. E. Grinstead, OSRD 4517, 
OEMsr-1121, Report PI-123, Nov. 15, 1944. 

Div. 17-312-M3 

24. The Design and Development of the Inductor Com¬ 
pass, C. E. Grinstead, OSRD 5064, OEMsr-1121, 
Summary Report PI-131, May 23, 1945. 

Div. 17-312-M4 

24a. Ibid., pp. 3-5. 

INTERNATIONAL BUSINESS MACHINES 
CORPORATION 

25. Airborne Odograph, Preliminary Bulletin on Model 
AO-3, Operation and Compensation. 

Div. 17-313.11-M6 

26. Airborne Odograph, Alfred B. Benson, OSRD 5396, 
OEMsr-426, July 31, 1945. Div. 17-313.11-M5 

27. Development Report, Land Odograph, W. W. Mc¬ 
Dowell, C. D. Lake, and G. F. Daly, OEMsr-426, 
NDRC Research Project PDRC-641, April 1943. 

Div. 17-313.12-M2 

MISCELLANEOUS 

28. Odographs, Course Plotters or Dead-Reckoning 

Tracers (Summary Report), OSRD 1582, July 15, 
1943. Div. 17-313-MI 


29. Aircraft Compasses, Operation and Flight Instruc¬ 
tions for Gyro Flux Gate Compass, Technical 
Order 05-15-27, Jan. 31, 1944. 

30. Gyro Stabilized Flux Gate Compass System, Hand¬ 
book of Operation and Service Instructions AN 
05-15-16, April 15, 1944, Revised May 20, 1944. 

Div. 17-311-M2 

31. Air Position Indicators and Associated Com¬ 
ponents, J. P. Palmer and W. F. Wright, Radia¬ 
tion Laboratory Report 63, MIT, June 18, 1944. 

32. Pioneer Gyro Flux Gate Compass System, Opera¬ 
tions and Service Instructions, Report 45-16D, 
Bendix Aviation Corporation, 1944. 

Div. 17-311-MI 

33. The Air Mileage Unit, S. D. 0342. (Photostat) 

34. Operating Instruction Manual, War Department 
Technical Manual TM-5-9411, Prepared by Inter¬ 
national Business Machines Corporation. 

35. Operating Instruction Manual, War Department 
Technical Manual TM-5-9401, Prepared by Monroe 
Calculating Machine Company. 

35a. Ibid., pp. 53-64. 

36. Odograph Installations in Ferrets Nos. 7 and 

8 [in the] Southivest Pacific Area, Frank F. Weber 
and William Finley Wright, Technical Observers, 
Section 22, U. S. Army Air Forces, General Head¬ 
quarters, Southwest Pacific Area, Revised Nov. 4, 
1944. Div. 17-313.11-M4 


Chapter 2 

1. Synchronization of Photoflash Bombs, Allen A. 

Walsh, C. W. Turner, and E. Dudley Goodale, 
OSRD 3626, OEMsr-1256, Service Project OD-141, 
NBC, June 15, 1944. Div. 17-323.4-MI 

2. Synchronization of Photoflash Bombs, Allen A. 

Walsh and J. Lewis Hathaway, OSRD 4893, 
OEMsr-1256, Service Project OD-141, NBC, Mar. 
20, 1945. Div. 17-323.4-MI 

3. Synchronization of Photoflash Bombs (Final Re¬ 
port), Allen A. Walsh and J. Lewis Hathaway, 
OSRD 5675, OEMsr-1256, NBC, Sept. 24, 1945. 

Div. 17-323.4-M2 

Buckley Field Tests [of] T-58 Fuze Equipment 
(Supplementary Report), Allen A. Walsh, J. Lewis 
Hathaway, and Vernon J. Duke, OSRD 5675, 
OEMsr-1256, NBC, Oct. 31, 1945. 

Div. 17-323.4-M3 

4. Characteristic Sheet of Mechanical Time Arming 
Delay, T4, O.P. No. 3589, Aberdeen Proving 
Ground, Aberdeen, Md., July 6, 1945. 

5. Aberdeen Proving Ground Firing Record B-8934, 
with APG Photograph A-28047; June 12, 14, and 
15, 1945. 

6. Static Synchronization Tests of T58 Fuze and 
M46 Photoflash Bomb, Aberdeen Proving Ground, 
Aberdeen, Md., August 1945. 






BIBLIOGRAPHY 


175 


Chapter 3 

1. “The Oximeter, an Instrument for Measuring Con¬ 
tinuously the Oxygen Saturation of Arterial Blood 
in Man,” Glenn A. Millikan, Review of Scientific 
Instruments, Vol. 13, No. 10, October 1942, pp. 
434-444. 

2. “Improved Form of Sensitive Relay,” Victor 
Legallais, Review of Scientific Instruments, Vol. 
14, No. 1, January 1943, p. 51. 

3. Oxygen-Want Indicator and Flight Research Oxim¬ 

eter, OSRD 1643, OEMsi - -12 and OEMsr-544, Uni¬ 
versity of Pennsylvania and Central Scientific 

Company, Jan. 1, 1944. Div. 17-321-MI 

4. Oxygen-Want Indicator, K. H. Booty, OSRD 3854, 

OEMsr-544, Central Scientific Company, July 31, 
1944. Div. 17-321-M2 

5. Oximeters for Use in Aircraft, Glenn A. Millikan, 

OSRD 6429, OEMsr-12, University of Pennsyl¬ 
vania, January 1946. Div. 17-321-M3 

5a. Ibid., p. 10. 

5b. Ibid., pp. 19-21. 

5c. Ibid., p. 30. 

5d. Ibid., pp. 32-34. 


Chapter 4 

1. Radio Time Comparator, W. F. Priest, OEMsr- 

1448, OSRD 5042, Hughes Aircraft Company, 
September 1945. Div. 17-323.81-MI 

2. The XA-2 Zenith Camera, George H. Bateman, 
Peter Krause, J. Carroll, and M. Glicken, U. S. 
Army Air Forces Computation Section, 7th AAF 
Geodetic Control Squadron, 311th Reconnaissance 
Wing, Buckley Field, Colorado, November 1945. 

Div. 17-452-MI 

2a. Ibid., p. 21. 


Chapter 5 

1. Review of Methods of Measuring the Contents of 
Fuel Tanks, F. Postlethwaite, OSRD Liaison Office 
II-5-7409(S), Technical Note Inst-756, Royal Air¬ 
craft Establishment, Great Britain, March 1943. 

Div. 17-322.1-MI 

2. Simmonds Capacitor Fuel Contents Gauge, G. E. 
Bennett and E. C. Voss, OSRD Liaison Office II- 
5-7408(S), Technical Note Inst-757, Royal Air¬ 
craft Establishment, Great Britain, March 1943. 

Div. 17-322.1-M2 

3. Development of Electric Frequency Meter or 
Tachometer, L. L. Nettleton, OEMsr-266, Final 
Progress Report D3-264, Gulf Research and De¬ 
velopment Company, Aug. 10, 1942. 

Div. 17-323.82-MI 


4. An Acoustic Volume-Measuring Device, W. Cay- 
wood, OSRD 5166, OEMsr-1234, Carnegie Institute 
of Technology, May 31, 1945. Div. 17-322.1-M4 
4a. Ibid., pp. 16-18. 

5. Aircraft Fuel Quantity Gauge (Parts I and II), 

William G. Fastie and Joseph Razek, OSRD 5672, 
OEMsr-178 and OEMsr-266, Johns Hopkins Uni¬ 
versity and Gulf Research and Development Com¬ 
pany, Oct. 31, 1945. Div. 17-322.1-M5 

5a. Ibid., pp. 1-13. 

5b. Ibid., pp. 14-72. 

5c. Ibid., pp. 73-79. 

6. Some Characteristics of Aircraft Engine Fuels , 

Their Influence on Capacitor-Type Tank Gauges , 
Paul G. Exline and J. W. Dashiell, OSRD 4016, 
OEMsr-266, Gulf Research and Development Com¬ 
pany, June 30, 1944. Div. 17-322.1-M3. 

6a. Ibid., pp. 8-9. 

6b. Ibid., p. 30. 


Chapter 6 

1. Combustion Efficiency Indicator Investigation , 
W. E. Stephens, OEMsr-267, Progress Report D3- 
258, University of Pennsylvania. 

Div. 17-322.2-M9 

2. Combustion Control, Carl S. Carlson, OEMsr-267, 
University of Pennsylvania. Div. 17-322.2-MI 

3. An Instrument for Measuring Combustion Effi¬ 

ciency, Carl S. Carlson, OEMsr-267, Progress Re¬ 
port D3-296, University of Pennsylvania, Oct. 3, 
1942. Div. 17-322.2-M2 

4. An Instrument for Measuring Combustion Effi¬ 
ciency, Carl S. Carlson and Miller J. Sullivan, 
OEMsr-267, Progress Report D3-335, University of 
Pennsylvania, Dec. 1, 1942. Div. 17-322.2-M2 

5. The Development of an Instrument to Increase 
Combustion Efficiency, Carl S. Carlson and Miller 
J. Sullivan, OSRD 1237, OEMsr-267, University of 
Pennsylvania, Feb. 1, 1943. Div. 17-322.2-M3 

6. The Development of an Instrument to Increase 
Combustion Efficiency, Carl S. Carlson and Miller 
J. Sullivan, OSRD 1471, OEMsr-267, University of 
Pennsylvania, Apr. 1, 1943. Div. 17-322.2-M4 

7. The Develo'irment of an Instrument to Measure 
Combustion Efficiency Aboard Naval Vessels, Carl 
S. Carlson and Miller J. Sullivan, OEMsr-267, 
University of Pennsylvania, June 1, 1943. 

Div. 17-322.2-M7 

8. Studies and Experimental Investigations in Con¬ 

nection with the Develojnnent of an Instrument for 
Use in Measuring Combustion Efficiency in Naval 
Vessels, Carl S. Carlson and Miller J. Sullivan, 
OSRD 3144, OEMsr-267, University of Pennsyl¬ 
vania, Nov. 30, 1943. Div. 17-322.2-M8 

8a. Ibid., Appendix 5. 

8b. Ibid., pp. 15-18, and Appendix 2. 

8c. Ibid., pp. 18-20 and Appendices 3 and 4. 


CONFIDENTIAL 






176 


BIBLIOGRAPHY 


Chapter 7 

1. Supersonic Signalling, Harold K. Schilling, OSRD 
4219, OEMsr-1210, Sei'vice Projects SC-105 and 
17.3-21, Pennsylvania State College, Sept. 18, 1944. 

Div. 17-436.45-MI 

2. Supersonic Signalling in the Tropics, Harold K. 

Schilling, OSRD 4496, OEMsr-1210, Service 

Projects SC-105 and 17.3-21, Pennsylvania State 
College, Dec. 16, 1944. Div. 17-436.45-M2 

3. Ultrasonic Signalling, Harold K. Schilling, OSRD 
5012, OEMsr-1210, Service Projects SC-105 and 
17.3-21, Pennsylvania State College, Mar. 31, 1945. 

Div. 17-436.45-M3 


Chapter 8 

1. Energy Distribution in Machine Gun Sounds, J. P. 
Maxfield, OSRD 1727, OEMsr-498, Service Project 
SC-27, Bell Telephone Laboratories, July 21, 1943. 

Div. 17-422-MI 

2. The Character of Sounds from Army Vehicles, 

F. K. Harvey, G. F. Hull, Jr., R. T. Jenkins, J. B. 
Kelly, and N. G. Wade, OSRD 4254, OEMsr-498, 
Service Project SC-27, Bell Telephone Laboratories, 
Aug. 21, 1944. Div. 17-421-MI 

3. Jungle Acoustics, Carl F. Eyring, OSRD 4699, 
OEMsr-1335, Service Project SC-105, Rutgers Uni¬ 
versity, Feb. 15, 1945, Figure 1. Div. 17-411.2-MI 
3a. Ibid., p. 4. 

3b. Ibid., p. 38, Appendix C. 

3c. Ibid., p. 7, Appendix A. 

3d. Ibid., pp. 10-15. 

3e. Ibid., p. 33. 

3f. Ibid., p. 23. 

3g. Ibid., p. 64. 

3h. Ibid., pp. 36-61 and Figures 38-66. 

4. Recordings of Jungle Sounds, Carl F. Eyring, 
OSRD 4704, OEMsr-1335, Service Project SC-105, 
Rutgers University, Feb. 17,1945, p. 2 and Figure 1. 

Div. 17-411.2-M2 

4a. Ibid., pp. 6-14. 

4b. Ibid. This report gives an annotated list of the 
species of birds, mammals, amphibians, and in¬ 
sects studied. Two edited records accompany 
this report; the original records are being pre¬ 
served. 

5. “The Absorption of Sound in Gases,” Vern 0. 
Knudsen, The Journal of the Acoustical Society of 
America, April 1935. 

6. “The Absorption of Sound in Air, in Oxygen, and 
in Nitrogen, Effects of Humidity and Tempera¬ 
ture,” Vern 0. Knudsen, The Journal of the 
Acoustical Society of America, October 1933. 


7. Sonic Deception, The Reproduction, Transmission 
and Reception of Deceptive Somids, OSRD 4094, 
OEMsr-908, BTL, Western Electric Co., Dec. 15, 
1944. 

8. “Auditory Patterns,” Harvey Fletcher, Review of 
Modern Physics, Vol. 12, January 1940, pp. 47-65. 

9. Masking Experiments, NDRC 6.1-sr30-1757, Serv¬ 
ice Projects NO-163 and NS-164, [Part] II, Re¬ 
port U-258, UCDWR, Sept. 15, 1944. 

Div. 6-560.21-M6 


Chapter 9 

1. The Measurement of the Attenuation of Sound 
Waves of Finite Amplitude, Harvey Fletcher, July 
9, 1941. 

2. Attenuation of Intense Sound in the Atmosphere, 
Vern O. Knudsen, R. W. Leonard, and others, 
OSRD 384, University of California, Dec. 31, 1941. 

Div. 17-431-MI 

3. “Absorption of Sound in Gases,” Vern O. Knudsen, 
The Journal of the Acoustical Society of America, 
Vol. 6, April 1935, p. 199. 


Chapter 10 

1. Physiological Effects of Exposure to Certain 
Sounds (Final Report), Hallowell Davis, Robert 
Galambos, Joseph E. Hawkins, Jr., Horace O. 
Parrack, Moses H. Lurie, and Jeannette C. Leigh¬ 
ton, OSRD 889, OEMsr-119, Harvard University, 
July 31, 1942. 

See also Effect of Sound on Man and Means for 
Producing Such Sound, OSRD 1255, Nov. 9, 1942. 

Div. 17-435.21-MI 

2. Temporary Deafness Following Exposure to Loud 
Tones and Noise, Hallowell Davis, Clifford T. 
Morgan, and others, OEMcmr-194, Harvard Medi¬ 
cal School, Sept. 30, 1943. Div. 17-435.21-M2 

3. Injury to the Inner Ear Produced by Exposure to 

Loud Tones (Supplementary Report), Joseph E. 
Hawkins, Jr., Moses H. Lurie, and Hallowell Davis, 
OEMcmr-194, Harvard Medical School, Dec. 31, 
1943. Div. 17-435.21-M3 


Chapter 11 

1. Effect and Production of Noise, Robert M. Jones, 
Max Kupferberg, Joseph McCord, Earl F. Pound, 
Harry E. Geib, and Gerard S. Mercurio, OSRD 
Report, OEMsr-197, Service Projects OD-110, SC- 
47, and CE-39, Stevens Institute of Technology, 
Oct. 31, 1945, p. 48. 


/ C QNFJDFjNTI AL T 







BIBLIOGRAPHY 


177 


Chapter 12 

1. Effect and Production of Noise, Robert M. Jones, 
Max Kupferberg, Joseph M. McCord, Earl F. 
Pound, Harry E. Geib, and Gerard S. Mercurio, 
OSRD Report, OEMsr-197, Service Projects OD- 
110, SC-47, and CE-39, Stevens Institute of 
Technology, Oct. 31, 1945, p. 108. 

la. Ibid., Figure 1, p. 60. 

lb. Ibid., p. 127. 

lc. Ibid., p. 86. 

l d. Ibid., p. 187. 

2. Studies and Experimental Investigations in Con¬ 
nection with the Development of Sound Sources 
(Final Report), OSRD 1728, OEMsr-146, Army 
Project SC-4, Western Electric Co., June 15, 1943. 


Chapter 13 

1. Sonic Deception, The Rejrroduction, Transmission 
and Perception of Deceptive Sounds, OSRD 4094, 
OEMsr-908, BTL, Western Electric Co., Dec. 15, 
1944. 

2. Radio Remote Control Device, Earl F. Pound, 
OSRD Report, OEMsr-197, Service Project SC-47, 
Stevens Institute of Technology, Oct. 31, 1945. 

3. Water Heater, Acoustical and Timing System, 
OSRD 4906, OEMsr-908, Service Project NR-104, 
BTL, Western Electric Co., Apr. 15, 1945. 

4. Water Heater, D. F. Warner, OSRD 4907, OEMsi'- 
1230, Service Project NR-104, General Electric Co., 
Apr. 16, 1945. 


VFIDENTIAL 





OSRD APPOINTEES 

DIVISION 17 


Chiefs 

George R. Harrison 
Paul E. Klopsteg 


Deputy Chiefs 

E. A. Eckhardt 
Paul E. Klopsteg 


Technical Aides 

Miles J. Martin Clark Goodman 

Francis L. Yost John A. Hornbeck (WOC) 

Members 

0. S. Duffendack 
Theodore Dunham, Jr. 

E. A. Eckhardt 
Harvey Fletcher 

Melville I. Stein 

section 17.1 

Chief 

E. A. Eckhardt 

Deputy Chief 

Herbert E. Bragg 

Spec. Asst, to Chief 

John A. Hornbeck 

Technical A ide 

Herbert E. Bragg 

Members 

Charles B. Bazzoni Semi J. Begun 

J. M. Cork 


William E. Forsythe 
George R. Harrison 
Herbert E. Ives 
Brian O’Brien 


178 


CONFIDENTIAL 




OSRD APPOINTEES 


179 


SECTION 17.2 

Chief 

Melville I. Stein 


Technical Aide 

George E. Beggs 


Gioacchino Failla 


Members 

C. H. Willis 


section 17.3 

Chief 

Harvey Fletcher 

Spec. Asst, to Chief 

William S. Gorton 
L. J. Sivian 

Acting Chief 

P. M. Morse 

Technical A ides 

William S. Gorton (WOC) 

Members 

Davis Hallowell 
Floyd A. Firestone 

E. C. Wente 


J. C. Hubbard 


Clifford Morgan 


Vern 0. Knudsen 
Stanley S. Stevens 


0NFIDENT1AL 






CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS 


The contract information given below is for Division 17 work reported in (or related to) this 
volume. Contract information associated with Division 17 work reported in other volumes of the 
Division 17 Summary Technical Report is given in those volumes. 


Contract 

Name and Address 


Number 

of Contractor 

Subject 

NDCrc-97 

Gulf Research and Development Company 
Pittsburgh, Pennsylvania 

Studies and experimental investigations in 
connection with the development of a 
telemetric device for measurement of the 
rate of flow of fluids, etc., embodying the 
use of thermistors. 

NDCrc-187 

Carnegie Institution of Washington 
Washington, D. C. 

Studies and experimental investigations in 
connection with (i) problems, such as 


those of magnetic compensation, and of 
optimum location, arising in conjunction 
with the use of magnetic compasses in 
tanks and other vehicles; (ii) similar 
problems which may arise in conjunction 
with the use of magnetic compasses in 
naval craft; (iii) continued consultation, 
tests, and redesign of vehicular 
odographs, marine odographs, and air¬ 
craft odographs, pedographs, and dead 
reckoning tracers generally; (iv) the de¬ 
velopment of a detonating mechanism for 
use with explosive charges, which mechan¬ 
ism is to be actuated by the magnetic 
field of a tank or other vehicle; (v) the 
study of the magnetic characteristics of 
vehicles, or naval craft, when necessary 
in connection with (i), (ii), (iii), and 
(iv) hereof; (vi) the development of a 
detector for magnetic masses, such de¬ 
tector to be free of any substantial ex¬ 
ternal field of its own; and (vii) such 
other related problems as may arise from 
time to time. 


OEMsr-12 The Trustees of the University of 

sylvania 

Philadelphia, Pennsylvania 


OEMsr-151 Carnegie Institution of Washington 

Washington, D. C. 


Penn- Studies and experimental investigations in 
connection with the improvement of in¬ 
struments for measuring the oxygen 
saturation of blood in personnel operating 
military vehicles. 

Studies and experimental investigations in 
connection with (i) the magnetic field at 
various depths beneath and around tanks 
and motorized vehicles, (ii) the effects of 
deperming and degaussing on these 
magnetic fields, (iii) the most suitable 
location for degaussing coils on motorized 
vehicles from practical and theoretical 
points of view, (iv) the development of a 
mechanism operated by the magnetic 
fields of vehicles suitable for the dis¬ 
charge of land mines to test the effective¬ 
ness of protection, and (v) the develop¬ 
ment of a method of detecting land mines 
in ferro-magnetic cases, particularly such 
methods as may be employed in connec¬ 
tion with the operation of motorized 
units. 


180 









CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS— (Continued) 


Contract Name and Address 

Number of Contractor 

Subject 

OEMsr-266 Gulf Research and Development Company 

Pittsburgh, Pennsylvania 

Studies and experimental investigations in 
connection with the development of (i) 
improved methods of submarine mine con¬ 
trol, (ii) a security device, (iii) an im¬ 
proved helium purity indicator for use in 
range-finders and lighter-than-air craft, 
(iv) a device for the determination of 
the quantity of fuel in the tanks of air¬ 
craft, (v) an indicator mine and as¬ 
sociated devices and methods for deter¬ 
mining the effectiveness of various 
explosive means of clearing minefields, 
and (vi) other instruments and devices 
of warfare when and as requested in 
writing by the Contracting Officer or an 
authorized representative. 

OEMsr-267 The Trustees of the University of Penn¬ 

sylvania 

Philadelphia, Pennsylvania 

Studies and experimental investigations in 
connection with the development of an 
instrument for use in measuring the 
combustion efficiency in naval vessels. 

OEMsr-340 Monroe Calculating Machine Company 

Orange, New Jersey 

Studies and experimental investigations in 
connection with (i) the design, develop¬ 
ment, fabrication, and testing of one or 
more full-scale models of an odograph; 
(ii) and the design, development, fabrica¬ 
tion, and testing of pilot models, suitable 
for production, of a remote reading com¬ 
pensated magnetic compass to provide 
direction indications for the odograph. 

OEMsr-426 International Business Machines Corpora¬ 

tion 

Endicott, New York 

Studies and experimental investigations in 
connection with (i) the design, develop¬ 
ment, fabrication, and testing of one or 
more full-scale models of an odograph, 
(ii) the redesign, construction, and test¬ 
ing of twelve (12) full-scale models of an 
aircraft odograph, and (iii) the redesign 
and manufacture of pilot units of said 
redesigned airborne odographs in such 
numbers as the Contractor and the Scien¬ 
tific Officer estimate can be prepared 
within the maximum amount of contract 
funds. 

OEMsr-544 Central Scientific Company 

Chicago, Illinois 

Studies and experimental investigations in 
connection with the development of a 
production model of the flight oximeter 
developed under Contract No. OEMsr-12. 

OEMsr-1121 General Motors Corporation, Research 

Laboratories Division 

Detroit, Michigan 

Studies and experimental investigations in 
connection with (i) the development of a 
remote indicating inductor compass, and 
(ii) means for demagnetizing tanks and 
other vehicles, and the effects thereof on 
compasses. 

CONFIDENTIAL 

i8i 










CONTRACT NUMBERS, CONTRACTORS, AND SUBJECT OF CONTRACTS— (Continued) 


Contract 

Number 

Name and Address 
of Contractor 

Subject 

OEMsr-1256 

Radio Corporation of America, RCA Victor 

Studies and experimental investigations in 


Division 

Camden, New Jersey 


connection with the development of radio 
control apparatus for the synchronous 
firing of one or more photoflash bombs in 
conjunction with airborne camera equip¬ 
ment which meets the majority of the 
military specifications as outlined by the 
representatives of the Ordnance Depart¬ 
ment; delivery and field testing of one 
hundred twenty-five (125) bomb i-eceiv- 
ing units, type T-58. 


OEMsi’-lMS Hughes Aircraft Company, a Division of 

the Hughes Tool Company, a Corpora¬ 
tion 

Culver City, California 


Studies and experimental investigations in 
connection with the (i) engineering of a 
radio chronometer comparator for time 
control of astronomic survey, including 
modification or redesign of radio receiver 
equipment to be used in conjunction with 
the chronometer comparator, and (ii) 
construction of three complete field test 
systems comprised of comparator circuits, 
radio receivers and antennae, all equip¬ 
ment to be small, rugged, suitable for 
use under extremely adverse conditions, 
and easily transportable. 


182 








SERVICE PROJECT NUMBERS 

The projects listed below were transmitted to the Executive 
Secretary, NDRC, from the War or Navy Department through 
either the War Department Liaison Officer for NDRC or the 
Office of Research and Inventions (formerly the Coordinator of 
Research and Development), Navy Department. 


Service 

Project 

Number 

Subject 

AC-48 

AC-80 

Army Projects 

Airborne odograph. 

The development of a simple light-weight and accurate flow 
meter for use as a flight and cruising control instrument in 
aircraft. 

AC-110 

Engineering of radio chronometer comparator for time control 
of astronomic survey. 

CE-18 

CE-28 

CE-28 Ext. 
OD-17 

Development of an odograph for military road reconnaissance. 
Vehicular remote-indicating compass. 

Compasses for armored vehicles. 

Determination of a suitable compass or direction indicating 
system for armored combat vehicles, including provision for 
repeater instruments for the driver, commander, and all 

OD-141 

gunners. 

Radio means for synchronization of aerial camera shutter and 
photoflash bombs. 

NA-153 

NA-154 

NS-96 

NS-124 

NS-170 

Navy Projects 

Simplified airborne odograph. 

Fuel quantity gauge. 

Development of a boiler flue gas indicator. 

Dead reckoning tracer for use on surface vessels. 

Design of magnetic compass equipment. 


CONFIDENTIAL 


183 



























INDEX 


The subject indexes of all STR volumes are combined in a master index printed in a separate volume. 
For access to the index volume consult the Army or Navy Agency listed on the reverse of the half-title page. 


Acoustic bomb, 113-116 
evaluation, 115 

intensity and rate of attenuation, 
114-115 

methods of combining explosions, 
113-114 

Acoustic fuel-measuring device, 75, 
76 

Acoustics of jungle 
see Jungle acoustics 
Aerial mapping instrument, 73-74 
Aerial photography 

see Photoflash bomb photography 
AES heater (Army Experimental 
Station loudspeaking sys¬ 
tem), 140-146 

dimensions and weights, 143 
loudspeakers, 144-146 
magnetic recorder-reproducer, 

143 

microphones and amplifiers, 143- 

144 

power supply, 146 
Air mileage devices, 24-26 
British unit, 25 

comparative summary of air¬ 
speed devices, 25-26 
impeller log, 25 
Pioneer pump unit, 25 
Schwien true airspeed meter, 25 
Airborne compass, 23-24 
Airborne integrator, 33-39 
air drift compensator, 34, 37 
components, 33-34 
plotting table, 37-38 
Aircraft fuel gauges, 75-79 

acoustic volume-measuring de¬ 
vice, 75, 76 

capacity type, 75, 78-79 
electric frequency meter and 
tachometer, 75-76 
hot-wire gauge, 75-78 
types of fuel, 78 

Airdrift compensator for inte¬ 
grator, 34, 37 
Airspeed indicators, 24-26 
British unit, 25 
comparative summary, 25-26 
impeller log, 25 
Pioneer pump unit, 25 
Schwien meter, 25 
Anoxia measuring instruments, 68- 
72 

evaluation, 72 


flight research oximeter, 68, 71 
oxygen want indicators, 68-71 
AO-3, airborne odograph, 39 
Army Experimental Station 
junior heater, 140-146 
sound transmission and recep¬ 
tion, 131-138 

Attack plotter, odograph equip¬ 
ment, 56 

Azimuth indicator for integrator, 
32 

Bell Telephone Laboratories 
magnetic recorder, 143 
siren for sonic deception, 128 
Boilers, combustion efficiency in¬ 
dicators 

see Combustion efficiency indi¬ 
cators, boilers 
Bomb, acoustic, 113-116 
evaluation, 115 

intensity and rate of attenuation, 
114-115 

methods of combining explosions, 
113-114 

Bomb receiver, photoflash bomb 
photography, 61, 64-65 
Breeze flowmeter, 75 
British 

air mileage unit, 25 
fuel gauges, 78 
Waymouth fuel gauge, 79 
Brush Development Company, 143 
BTL (Bell Telephone Laboratories) 
siren, sound masker, 128 

Canary motor sound simulator, 
123-126 

acoustic performance, 125-126 
as masking device, 128 
operation, 123-125 
Carbon dioxide recorders for com¬ 
bustion efficiency measure¬ 
ment, 80-83 
maintenance, 82-83 
reliability, 82 
types, 80, 82-83 

Carnegie Institution of Washing¬ 
ton, 4 

Central Scientific Company, 71 
“Charlie” (sound simulating de¬ 
vice) , 117 

Chronometer comparator, radio, 
73-74 


CMR (Committee on Medical Re¬ 
search), 110 

Coleman ear unit, oximeter, 71 
Combustion efficiency indicator,, 
boilers, 80-84 

carbon dioxide recorders, 81-83 
elimination of smoke, 80 
factors affecting combustion effi¬ 
ciency, 81 

flame brightness, 84 
military requirements, 80 
steam flow-oil flow ratio, 84 
Committee on Medical Research,. 
110 

Comparator, radio chronometer,. 
73-74 

Compass, aii'borne, 23-24 
Compass, magnesyn, 56 
Compass, vehicular odograph, 6-23 
comparison of compasses, 20 
compass followers, 7 
demagnetization of military ve¬ 
hicles, 10-13 
DTM compass, 13-17 
error compensation, 7-13 
gyroscopic compass, 6-7 
inductor compass, 17-23 
magnetic compass, 7-17 
reduction of vibration effects, 17 
Compass error compensation, 7-13: 
DTM compass, 14-17 
heeling and pitching errors, 9 
quadrantal error, 8-9 
semicircular error, 8 
subpermanent magnetization, 9- 
10 

Compass for landing craft, 56 
Course plotting instrument 
see Odograph equipment 

Deafness caused by noise, 110-112 
experiments with animals, 111- 
112 

hearing loss produced in humans, 
110-111 

Department of Terrestrial Mag¬ 
netism 

compass, 13-17 

experimental integrator, 28-30 
Diffraction in ultrasonic signaling, 
90 

Diplacusis (pitch perception), 110, 
111 




185 





186 


INDEX 


Disk drive integrator 

air drift compensator, 34, 37 
components, 33-34 
plotting table, 37-38 
Distance measuring instruments 
air mileage devices, 24-26 
sea logs, 26-27 

DTM compass (Department of 
Terrestrial Magnetism), 13- 
17 

error compensating system, 14-17 
servomechanism, 13-14 
DTM experimental integrator (De¬ 
partment of Terrestrial 
Magnetism), 28-30 
functions, 29-30 
interpolation by hunting, 29 
variable coupling element, 28-29 
variable map scale, 29-30 
Dynamotors for loudspeaking sys¬ 
tem, 155 

Electrical Products Research, Inc., 

135 

Eraser, magnetic, 11-13 

applications and tests, 11-13 
theory of operation, 11 
Explosions, effect of combining 
charges, 113-116 
evaluation, 115 

intensity and rate of attenuation, 
114-115 

methods of combining explosions, 
113-114 

Explosive sound characteristics, 
117-119 

effect of terrain, 119 
oscillograms, 117, 120-121 

Flash bomb photography 

see Photoflash bomb photography 
Flight research oximeter, 68, 71 
Flowmeter, Breeze, 75 
Fluxgate compass, 23-24 
Fort Hancock, N. J., 131 
Fuel gauges, aircraft, 75-79 

acoustic volume-measuring de¬ 
vice, 75, 76 

capacity type gauge, 75, 78-79 
electric frequency meter, 75-76 
hot-wire gauge, 75-78 
types of fuel, 78 
Fuze, photoflash 

see Photoflash bomb photography 

Gauges, aircraft fuel, 75-79 

acoustic volume-measuring de¬ 
vice, 75, 76 
capacity type, 78-79 


electric frequency meter and 
tachometer, 75-76 
hot-wire gauge, 76-78 
types of fuel, 78 
General Electric Company, 56 
GM (General Motors) Research 
Laboratory 

inductor compass, 17-23 
magnetic eraser, 10-13 
Gulf Research and Development 
Company, 78 
Gun simulators, 120-123 
large field pieces, 123 
machine gun, 122 
mortar fire, 123 
rifle fire, 122 
single shots, 120-121 
Gyroscopic compass, 6-7, 23-24 

Hallicrafter S-39 radio l’eceiver, 73 
Harvard University, 110 
Hays carbon dioxide recorder, 82 
Hearing loss produced by noise, 
110-112 

experiments with animals, 111- 
112 

in humans, 110-111 
Heaters for sound deception, 138- 
170 

experimental equipment, 138 
junior heater, 140-146 
remote control device, 146-148 
S2M heater, 138-140 
water heater, 148-170 
Hot-wire fuel gauge, 75-78 
electric circuit, 77 
HR (Hays carbon dioxide re- 
corder), 82 

Hughes Aircraft Company, 73 

IBM Company (International Busi¬ 
ness Machines), 30-38 
IBM disk drive integrator, 33-39 
air drift compensator, 34, 37 
components, 33-34 
plotting table, 37-38 
IBM ratchet drive integrator, 30- 
33 

azimuth indicator, 32 
magnetic deviation correction, 32 
scale changing, 32-33 
variable coupling, 30-32 
Impeller log (air mileage device), 
24 

Inductor compass, 17-23 
comparative tests with standard 
compasses, 40 
mu-metal core, 17 
performance tests, 20-23 


principles of operation, 17-18 
servomechanism, 18-20 
Integrators, odograph, 27-39 

DTM experimental integrator, 
28-30 

IBM disk drive aii’borne inte¬ 
grator, 33-39 

IBM ratchet drive integrator, 30- 

33 

requirements, 5, 27-28 
scotch yoke, 27-28 
International Business Machines 
Corporation, 30-38 
Intervalometer for photoflash bomb 
photography, 59, 62 

Johns Hopkins University, 77 
Jungle acoustics, 92-105 
ambient sounds, 96-99 
definition of terms, 93-94 
intensity level available for 
transmission loss, 100, 102 
judging sound direction, 98-99 
masking of ambient noise, 99- 
100 

micrometeorology in tropics, 102- 
105 

research apparatus, 92-93 
tactical problems, 99-102 
tests on various terrains, 94-96 
transmission loss measurements, 
92-96 

Junior heater (loudspeaking sys¬ 
tem), 140-146 

dimensions and weights, 143 
loudspeakers, 144-146 
magnetic recorder-reproducer, 

143 

microphones and amplifiers, 143- 

144 

power supply, 146 

Knudsen, terrain loss coefficients, 
94-95 

KS-12009 magnetic recorder, 143 

Landing craft compasses, 56 
LNR (Leeds and Northrup carbon 
dioxide recorder), 82-83 
Logs for odograph, 26-27 
impeller log, 25 

Loudspeaking systems, sonic decep¬ 
tion, 138-170 

experimental equipment, 138 
junior heater, 140-146 
remote control device, 146-148 
S2M heater, 138-140 
water heater, 148-170 

M-l standard compass, 40 


NFIDENTIAL 






INDEX 


187 


Machine gun simulators, 122 
Magnesyn compass, 56 
Magnetic airborne detector, use of 
odograph, 49 

Magnetic compasses, 7-17 

demagnetization of vehicles, 10- 
13 

DTM compass, 13-17 
sources of error, 8-10, 41-42 
Magnetic eraser, 10-13 

applications and tests, 11-13 
theory of operation, 11 
Magnetic fields of vehicles, 10-13 
magnetic eraser, 11-13 
measuring instrument, 10 
Magnetic recorder-reproducer 
AES loudspeaking system, 143 
S2M heater, 139 
water heater, 152, 154, 160 
Magnetization of compasses, sub¬ 
permanent, 9-10 

Magnetometer, remote-indicating, 
10 

Mapping instrument, aerial, 73-74 
Masking of sounds for enemy de¬ 
ception, 126-130, 136-138 
BTL siren, 128 
canary motor, 129 
jungle sounds, 99-100 
minimum masking noise, 136-137 
principles of masking, 127 
required intensity for deception, 
136-137 

sounds of vehicles, 126-130 
Meteorological equipment, ultra¬ 
sonic signaling, 88 
Meteorological study of jungle, 
102-105 

apparatus and definitions, 102- 
104 

equipment, 93 

humidity measurements, 105 
temperature data, 103-104 
terrain loss coefficients, 95-96 
wind velocity measurements, 104 
Mileage measuring instruments, 
24-27 

air mileage, 24-26 
sea logs, 26-27 

Monroe Calculating Machine Com¬ 
pany 

DTM compass, 13-17 
DTM experimental integrator, 
13-17 

Mortar fire simulation, 123 
Motor sound simulation, 123-126 
Multiphase intervalometer, photo¬ 
flash bomb photography, 59, 
62-63 


Naval Boiler and Turbine Labora¬ 
tory, 81 

Naval combustion efficiency indi¬ 
cator 

see Combustion efficiency indi¬ 
cator, boilers 

Naval Research Laboratox-y, 81 
Night photography of aerial bombs, 
58 

Noise, physiological effects, 110- 
112 

animals, 111-112 
humans, 110-111 
Noise in jungle 

ambient sounds, 96-99 
masking of ambient noise, 99-100 
Noise masking, sonic deception 
see Masking of sounds for enemy 
deception 

Odograph equipment, 5-57 
airborne compass, 23-24 
application to magnetic airborne 
detector, 49 

attack plotter for ships, 56 
integrators, 27-39 
mileage and speed devices, 24-27 
pedograph, 5, 52-55 
portable, 52-56 
power supply, 56 
inquired elements, 5-6 
step-writer, 5, 52-55 
vehicular compass, 6-23 
Odograph test installations, 5, 39- 
49 

aircraft, 39, 46-52 
amphibious truck, 44-46 
half-track, 43 
jeep, 40-41 
snow vehicles, 43 
tanks, 41-43 
Odometers, 24-27 
air mileage, 24-26 
sea logs, 26-27 
Orsat apparatus, 82 
“Oscar” (dummy paratrooper), 
117 

Oximeters, 68-72 
evaluation, 72 

flight research oximeter, 68, 71 
oxygen want indicators, 68-71 
Oxygen saturation measurement 
see Oximeters 

Oxygen want indicator, 68-71 
ear unit, 69 

pointer indicator, 69-70 
signal light indicators, 70-71 

Parabolic reflectors, ultrasonic 
signaling, 88 


Pedograph, 5, 52-55 
Pennsylvania State College, 87 
Photoflash bomb photography, 58- 
67 

bomb x’eceiver, 61, 64-65 
characteristics of apparatus, 65- 
67 

field tests, 61-62 
general description, 59-62 
military requirements, 58-59 
multiphase intei’valometer, 59, 
62-63 

night photography, 58 
radio transmitter, 61, 64 
synchronizer, 60, 63-64 
Physiological effects of noise, 110- 
112 

animals, 111-112 
humans, 110-111 
Pine Camp, New York, 131 
Pioneer Instrument Company 
gyrostabilized fluxgate compass, 
23 

pump unit, 25 
Pitch perception, 110, 111 
Pitot tube for airspeed indicator, 
25 

Pointer indicator, oxygen satura¬ 
tion, 69-70 

Primacord as a gun sound simu¬ 
lant, 121 

Psychological factors in sonic de¬ 
ception, 170 

Public addi’ess systems, sonic de¬ 
ception, 138-170 
experimental equipment, 138 
junior heatei', 140-146 
remote control device, 146-148 
S2M heater, 138-140 
water heater, 148-170 

RA 277 sound frequency analyzer, 

135 

Radio chi-onometer comparator, 73- 
74 

Radio transmitter, photoflash bomb 
photography, 61, 64 
Ranarex carbon dioxide recorder, 
80, 82-83 
evaluation, 83 

suggested improvements, 83 
Ratchet drive integrator, 30-33 
azimuth indicator, 32 
magnetic deviation connection, 32 
scale changing, 32 
variable coupling, 30-32 
RC models for heaters (remote 
conti’ol), 146-148 
models 2 and 3, 147-148 
l'equii’ements, 146-147 





188 


INDEX 


Receivers 

photoflash bomb photography, 
60, 67 

ultrasonic signaling, 87 
Recorders 

carbon dioxide, 81-83 
magnetic, 139-143, 152-154, 160 
Reflectors for ultrasonic signaling, 
87 

Refraction of sound rays, 133-134 
Rifle simulators, 122 
Royal Aircraft Establishment, 78 
Rozek hot-wire gauge, 77 
RR (Ranarex carbon dioxide re¬ 
corder) , 80, 82-83 
Rutgers University, 92 

S2M heater (loudspeaking system), 
138-140 

dimensions and weights, 138 
performance, 140 
S-39 radio receiver, 73 
Schwein true airspeed meter, 25 
Sea logs, 26-27 

Servomechanisms for compasses 
DTM compass, 13-14 
inductor compass, 18-20 
Signal light indicators, oxygen 
saturation, 70-71 
Simulation of sound 
see Sound simulation 
Sonic deception, 117-170 

masking noise and reception, 
136-138 

masking sounds of military ve¬ 
hicles, 126-130 

mobile loudspeaking systems, 
138-170 

psychological factors, 170 
sound simulation, 117-126 
sound transmission and reception 
studies, 131-138 
tactical consideration, 170 
techniques of sound recording, 
131-132 

Sound absorption, 106, 134 
Sound apparatus, jungle acoustics, 
93 

Sound attenuation, 106-108 
Sound characteristics, explosive, 
117-119 

effect of terrain, 119 
oscillograms, 117, 120-121 
Sound frequency analyzer, 135 
Sound masking, sonic deception 
see Masking of sounds for enemy 
deception 

Sound propagation characteristics, 
133-135 

loss of energy, 133 


refraction of sound rays, 133- 

134 

Sound ranging on simulated 
sounds, 121-122 

Sound recording techniques, 131- 

132 

Sound simulation, 117-126 

character of explosive sounds, 
117-119 

detection by sound-ranging 
equipment, 121-122 
listening tests, 121 
machine guns, 122 
motor sounds, 123-126 
rifle fire, 122 

Sound transmission, 87-109, 131- 
138 

jungle acoustics, 92-105 
meteorological conditions, 132- 

133 

propagation characteristics, 133- 

135 

sound source, 131-132 
ultrasonic signaling, 87-91 
Sound transmission loss, 106-109, 
133-135 

absorption by vegetation, 134 
absorption in air, 134 
absorption of waves of finite 
amplitudes, 106 

attenuation of waves of small 
amplitudes, 106-108 
influence of terrain, 108-109 
temperature and wind refrac¬ 
tion, 109 

temperature gradient, 133 
wind velocity gradient, 133-134 
Speed measuring devices, 24-27 
air mileage instruments, 24-26 
sea logs, 26-27 

Stavrokov (log pickup unit), 45 
Step-writer, 5, 52-55 
Stevens Institute Canary, 129 
Subpermanent magnetization in 
compasses, 9-10 
Supersonic signaling 

see Ultrasonic signaling 
Synchronizer, photoflash bomb 
photography, 60, 63-64 

T-4 mechanical arming device, 
photoflash bomb, 67 
T-58 photoflash fuze 

see Photoflash bomb.photography 
Tanks, effect on magnetic com¬ 
passes, 41-42 

Temperatui'e fluctuation, definition, 
102 

Temperature gradient, definition, 
94, 132 


Temperature profiles, definition, 
94 

Temperature refraction, 109 
Terrain loss, definition, 93-94 
Transformer compass, 17-23 

comparative tests with standard 
compasses, 40 
mu-metal core, 17 
performance tests, 20-23 
principles of operation, 17-18 
servomechanism, 18-20 
Transmission loss in jungle acous¬ 
tics, 93-96 

see also Sound transmission loss 
definition of terms, 93-94 
intensity level, 100, 102 
research apparatus, 93 
tests on various terrains, 94-96 
Transmitter, photoflash bomb 
photography, 61, 64 

Ultrasonic signaling, 87-91 
conclusions, 90-91 
diffraction, 90 

meteorological equipment, 88 
optimum weather conditions, 90 
parabolic reflectors, 87 
range measurements, 88-89 
receivers, 87 

research equipment, 87-88 
transmission measurements, 88- 
90 

University of Pennsylvania, 81 

Vehicles, magnetic fields, 10-13 
magnetic eraser, 11-13 
measuring instrument, 10 
Vehicles, sound masking, 126-130 
BTL siren, 128 
canary, 128 

evaluation of deceptive instru¬ 
ments, 129-130 

intensity of group of vehicles, 
127 

principles of masking, 127 
Vehicular odograph compass 

see Compass, vehicular odograph 

Water heater (loudspeaking sys¬ 
tem), 148-170 

acoustic and timing system, 149- 
162 

amplifier, 154 

anchoring mechanism, 165-166 
attenuator, 158, 162 
dynamotors, 155 
electric circuits, 150-152 
elevator mechanism, 166-167 
firing circuit, 168 
loudspeaker, 156-158 






INDEX 


189 


operation, 168-170 
orientation mechanism, 167-168 
performance, 148 
power supply, 163 
propulsion equipment, 163 
recorder, 160 


reproducer, 152, 154 
timing mechanism, 152-153, 158- 
160 

Waymouth fuel gauge, 79 
Wind gustiness, definition, 103 
Wind refraction, 109 


Wind velocity gradient, definition, 
94, 132 

Wind velocity variability, defini¬ 
tion, 102 

XA-2 Zenith camera, 73 


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